This moves the firstKey function from the sidebar-content into
the selection store module.

Bump @octokit/rest from 16.26.0 to 16.27.0

Bump raven-js from 3.27.0 to 3.27.1

Bump express from 4.17.0 to 4.17.1

Bump @babel/core from 7.4.4 to 7.4.5

Bump @babel/preset-env from 7.4.4 to 7.4.5

Bump core-js from 2.6.6 to 2.6.9

Bumps [express](https://github.com/expressjs/express) from 4.17.0 to 4.17.1.
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/master/History.md)
- [Commits](https://github.com/expressjs/express/compare/4.17.0...4.17.1)

Bumps [raven-js](https://github.com/getsentry/raven-js) from 3.27.0 to 3.27.1.
- [Release notes](https://github.com/getsentry/raven-js/releases)
- [Changelog](https://github.com/getsentry/sentry-javascript/blob/master/CHANGELOG.md)
- [Commits](https://github.com/getsentry/raven-js/commits)

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 16.26.0 to 16.27.0.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v16.26.0...v16.27.0)

Bumps [@babel/core](https://github.com/babel/babel) from 7.4.4 to 7.4.5.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/compare/v7.4.4...v7.4.5)

Bumps [@babel/preset-env](https://github.com/babel/babel) from 7.4.4 to 7.4.5.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/compare/v7.4.4...v7.4.5)

Bumps [core-js](https://github.com/zloirock/core-js) from 2.6.6 to 2.6.9.
- [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/v2.6.6...v2.6.9)

[Security] Bump tar from 2.2.1 to 2.2.2

Bumps [tar](https://github.com/npm/node-tar) from 2.2.1 to 2.2.2. **This update includes security fixes.**
- [Release notes](https://github.com/npm/node-tar/releases)
- [Commits](https://github.com/npm/node-tar/compare/v2.2.1...v2.2.2)

Format gulpfile.js and files in scripts/ using Prettier

Eliminate an inconsistency in the client codebase that most files are
formatted with Prettier but files in scripts/ and gulpfile.js were not.

Show focus indicator on various UI elements if they have keyboard focus

Bump express from 4.16.4 to 4.17.0

Bump prettier from 1.17.0 to 1.17.1

Bump @octokit/rest from 16.25.4 to 16.26.0

Bump codecov from 3.4.0 to 3.5.0

Bump core-js from 2.6.5 to 2.6.6

Bumps [prettier](https://github.com/prettier/prettier) from 1.17.0 to 1.17.1.
- [Release notes](https://github.com/prettier/prettier/releases)
- [Changelog](https://github.com/prettier/prettier/blob/master/CHANGELOG.md)
- [Commits](https://github.com/prettier/prettier/compare/1.17.0...1.17.1)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [express](https://github.com/expressjs/express) from 4.16.4 to 4.17.0.
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/master/History.md)
- [Commits](https://github.com/expressjs/express/compare/4.16.4...4.17.0)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 16.25.4 to 16.26.0.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v16.25.4...v16.26.0)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [core-js](https://github.com/zloirock/core-js) from 2.6.5 to 2.6.6.
- [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/v2.6.5...v2.6.6)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [codecov](https://github.com/codecov/codecov-node) from 3.4.0 to 3.5.0.
- [Release notes](https://github.com/codecov/codecov-node/releases)
- [Commits](https://github.com/codecov/codecov-node/commits)
Signed-off-by: dependabot[bot] <support@dependabot.com>

Enable a focus indicator for top bar buttons and the selected tab when
using keyboard input

The :focus-visible pseudo-class [1] enables showing or suppressing focus
outlines depending on the input modality, eg. hiding focus outlines by
default but enabling them if the user is using a keyboard or otherwise
indicates to their browser that they need a focus indicator.

It is not widely available natively yet though. Add the "official" JS
polyfill for it and a mixin that uses it to suppress an element's
outline when the user agent deems it is not required (typically when
using mouse input).

[1] https://developer.mozilla.org/en-US/docs/Web/CSS/:focus-visible

Implement new menu component and add icons for it

Incorporate build fix from https://github.com/hypothesis/client/pull/1127

Adjust the vertical offset of the content to match our previous dropdown
menus, which looked better.

This provides more flexibility as it can be used to set color as well as
size and it is also more consistent with how everything else is styled in the
application.

Replace the existing use of the `size` prop and tweak menu item icon
sizes.

Fix/simplify manifest rebuild when running "gulp watch"

On my system "gulp watch" was failing to generate the client's entry
point script `build/boot.js` correctly. This may have happened after
recent upgrades to gulp or Node.

The issue was that `generateManifest` was run after "gulp
watch" started, before build/scripts/boot.bundle.js was generated,
producing an empty output file in build/boot.js. It was not re-run later
after build/scripts/boot.bundle.js was generated.

After some experimentation, removing use of `gulp-batch` in the
`watch-manifest` task resolved the issue. I haven't verified whether the
node upgrade or a gulp upgrade was the root cause. Since gulp-batch was
non-essential, I've just removed it to simplify things and reduce the
risk of similar issues happening in future.

 - Add a clearer comment to explain what the global event listener
   effect is for
 - Add comment explaining what `ignoreNextClick` flag is for
 - Remove a test for the `ignoreNextClick` flag when a "click" event
   happens _outside_ of the menu toggle button. This _should_ close
   the menu
 - Use CSS classes to set menu alignment
 - Add some additional tests

The implementation is missing. It will be added in a follow-up PR.