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

- Update NotebookView to corral pagination, Notebook-y state
- Update NotebookResultCount to be dumber
  (to balance with PaginatedThreadList)
- Integrate PaginatedThreadList into NotebookView

Add a PaginatedThreadList component, which renders pagination controls.
This component is not yet hooked up to anything.

- Add a component to render pagination controls
- Component is unused

- Add a utility function for generating the right set of available
  pagination page numbers, given `currentPage`, `totalPages` and
  the maximum number of page options desired

- Make `Button` take `iconPosition` prop {`left|right`} to allow for
  right-aligned icons on buttons
- Add parameters to `button--labeled` mixin to allow for background
  color overrides

This test isn't meaningful as a number of other tests would fail if
sub-components were rendered without the presence of an `annotation`

Leave class naming alone for now, as these modules haven't been fully
normalized/component-ized yet.