The purpose of this PR is to be able to easily run karma tests in other
browsers without manually editing the karma configuration or making
local copies of the karma configuration.

Additions:

- `yarn test --no-browser` to avoid launching the default browser.
  It is up to the developer to run the tests in whatever browser she/he
  chooses by navigating to http://localhost:9876/.

- `yarn test --browser <browser>` run the tests in a different
  browser/s instead of the default browser. Chrome launcher comes by
  default with karma. Firefox, Safari and others can be installed
  independently.

Modifications:

- `yarn gulp test-watch` has been substituted by `yarn test --watch` for consistency.

The `disableShadowSidebar` flag and the corresponding behavior no longer
exists.

The `ToolbarController#getWidth` method started incorrectly returning 0
after 243c06d3. This commit moved the
content of the toolbar to a child of `ToolbarController._container` and
the `getWidth` method was not updated accordingly.

The incorrect result of `this.toolbar.getWidth()` in `Sidebar` later
resulted in an incorrect calculation of the sidebar's width and caused
`PdfSidebar` to think that the window was too narrow to support
side-by-side mode.

Fix the problem by updating `ToolbarController#getWidth` so that it
returns the correct value again.

Convert a statement into an if/else for readability.

- Remove `disableShadowSidebar` flag
- Simplify code structure
- Remove iframe from externalContainer on `destroy`.

Closes #2908

This prevents long lists from going off-screen and becoming unwieldy.

If the current user shows up in the filter list. (e.g they have annotations), then sort that user to the front of the list and add " (Me)" suffix to the end of the displayed name to make it easier for a user to find and filter their own annotations.

This small trick borrowed from
https://css-tricks.com/preventing-a-grid-blowout/ keeps the grid content
within the grid boundaries, thus improving the responsive design.

In a PR #3055, we remove reference to the plugin system for the
BucketBar and we create a property `bucketBar` in `Guest` class. I
overlook one of this reference in the `sidebar`.

This reverts commit 85f6023f.

This reverts commit e19983b0.

BucketBar is not used anymore as a plugin.

- Added types
- Moved out of the plugin directory
- Avoid extending from Delegator (unnecessary)

The sidebar component directs the opening of the notebook. This is for two reasons:

* it's a little bit easier to save the UI state of the current sidebar
  (immediately before the notebook is opened), in case in the future we
  want to restored it.

* to avoid adding additional events, like `show/hideSidebarControls`,
  that probably would be needed for granular control of the sidebar, in
  case the notebook would be directing the process of closing/re-opening
  the sidebar.

Because I am planning to introduce another method to hide the controls,
I renamed the hide/show methods in the sidebar and notebook components
to open/close. I also feel it describes better the visual outcome.

For consistency, I renamed the show/hideNotebook to open/closeNotebook.

Moved the user-filter below the heading and added a little bit of top
and bottom space.

Rename CSS class names for `Toolbar` component to match the component itself.
This component name is really overly generic but at least this brings
the CSS and Preact components into line.

One of the toolbar's classes was applied to a container element created
by `ToolbarController`. This class has been moved to an element created
by the `Toolbar` component for consistency. This means there is an
apparently redundant (no styling, one child) container div when looking
at the DOM structure for the toolbar + bucket bar. This will go away if
the whole sidebar container is made into a single Preact component in
future.

Rename all CSS classes used by the `AdderToolbar` component to follow
the `Component__element--modifier` syntax that we use for other
components. Also rename the `Adder.scss` file to match the Preact
component name.

This is not the correct solution, but as only one import is affected,
this is a simple workaround with no effect on other code.

Bumps [escape-string-regexp](https://github.com/sindresorhus/escape-string-regexp) from 1.0.5 to 4.0.0.
- [Release notes](https://github.com/sindresorhus/escape-string-regexp/releases)
- [Commits](https://github.com/sindresorhus/escape-string-regexp/compare/v1.0.5...v4.0.0)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [terser](https://github.com/terser/terser) from 5.5.1 to 5.6.0.
- [Release notes](https://github.com/terser/terser/releases)
- [Changelog](https://github.com/terser/terser/blob/master/CHANGELOG.md)
- [Commits](https://github.com/terser/terser/commits)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [core-js](https://github.com/zloirock/core-js) from 3.8.3 to 3.9.0.
- [Release notes](https://github.com/zloirock/core-js/releases)
- [Changelog](https://github.com/zloirock/core-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/zloirock/core-js/compare/v3.8.3...v3.9.0)
Signed-off-by: dependabot[bot] <support@github.com>

Because of recent changes in the sidebar (#2904), the BucketBar
component is no longer used as a plugin. @robertknight suggested to
remove all unneeded functionality.

Closes #2907

On PR #2904, it was forgotten to pass the bucket bar options to the
constructor.

Closes #3047

Remove entries that refer to dependencies that are no longer used by the
client or update restrictions that no longer apply. These were
automatically imported from Dependabot's config and never got pruned
when they became obsolete.

Bumps [typescript](https://github.com/Microsoft/TypeScript) from 4.1.3 to 4.1.5.
- [Release notes](https://github.com/Microsoft/TypeScript/releases)
- [Commits](https://github.com/Microsoft/TypeScript/compare/v4.1.3...v4.1.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [mocha](https://github.com/mochajs/mocha) from 8.2.1 to 8.3.0.
- [Release notes](https://github.com/mochajs/mocha/releases)
- [Changelog](https://github.com/mochajs/mocha/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mochajs/mocha/compare/v8.2.1...v8.3.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@sentry/browser](https://github.com/getsentry/sentry-javascript) from 6.1.0 to 6.2.0.
- [Release notes](https://github.com/getsentry/sentry-javascript/releases)
- [Changelog](https://github.com/getsentry/sentry-javascript/blob/master/CHANGELOG.md)
- [Commits](https://github.com/getsentry/sentry-javascript/compare/6.1.0...6.2.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [sass](https://github.com/sass/dart-sass) from 1.32.7 to 1.32.8.
- [Release notes](https://github.com/sass/dart-sass/releases)
- [Changelog](https://github.com/sass/dart-sass/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sass/dart-sass/compare/1.32.7...1.32.8)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@babel/preset-env](https://github.com/babel/babel/tree/HEAD/packages/babel-preset-env) from 7.12.13 to 7.12.17.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/main/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/commits/v7.12.17/packages/babel-preset-env)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.839.0 to 2.848.0.
- [Release notes](https://github.com/aws/aws-sdk-js/releases)
- [Changelog](https://github.com/aws/aws-sdk-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-js/compare/v2.839.0...v2.848.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 18.1.0 to 18.2.0.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v18.1.0...v18.2.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@babel/core](https://github.com/babel/babel/tree/HEAD/packages/babel-core) from 7.12.16 to 7.12.17.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/main/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/commits/v7.12.17/packages/babel-core)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

These custom names were a method of reducing the likelihood of these
elements being affected by the page's CSS. Since Shadow DOM support is
now much more ubiquitous this is not an issue, so switch back to
ordinary `<div>`s.

Note that the shadow hosts still use custom element names to prevent
them being impacted by page styles.  The elements being changed here are
inside the shadow DOM.

Add a new `/ui-playground` route to the client's dev server which hosts
a UI component playground/demo app, plus a link to this route on the dev
server homepage. The demo app provides a place to see and experiment with
UI components outside the context of the sidebar/notebook apps.

 - Add new `/ui-playground` route to dev server which serves a small
   Preact SPA

 - Add Preact SPA in `dev-server/ui-playground/` with a couple of
   placeholder "demos" for the `Button` and `Menu` components

 - Add configuration to gulpfile.js to build ui-playground JS and CSS
   bundles for Preact SPA