Move firstKey function from sidebar-content to store

Add utility to re-render components when store changes

 - Simplify an example. `useCallback` is not required.
 - Add a comment regarding effect cleanup

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

Fix an issue where `GroupListItem` components did not re-render when the
focused group changed. This component is due to be replaced shortly, so
this is really just a test case to show that `useStore` works as
expected.

Add a hook that connects a store to a React/Preact component and ensures that
it re-renders when relevant store state changes.

Merge pull request #1141 from hypothesis/dependabot/npm_and_yarn/babel-plugin-transform-async-to-promises-0.8.11

Bump babel-plugin-transform-async-to-promises from 0.8.10 to 0.8.11

This fixes a code generation bug which broke the latest version of
babel-plugin-transform-async-to-promises.

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

Bumps [babel-plugin-transform-async-to-promises](https://github.com/rpetrich/babel-plugin-transform-async-to-promises) from 0.8.10 to 0.8.11.
- [Release notes](https://github.com/rpetrich/babel-plugin-transform-async-to-promises/releases)
- [Commits](https://github.com/rpetrich/babel-plugin-transform-async-to-promises/compare/v0.8.10...v0.8.11)

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