Add react selection-tabs component

Only allow one group's submenu to be expanded at a time

 - Set `display: none` on the content of a Slider when it is fully
   collapsed, so that the DOM nodes are removed from keyboard navigation
   order

 - Make the collapse animation work more reliably across browsers by
   forcing a synchronous layout after changing the DOM node's height
   from "auto" to a fixed pixel size. In Chrome and Firefox neither
   `setTimeout(callback, 0)` nor `requestAnimationFrame` reliably
   ensured that the browser "saw" the change from "auto" =>
   fixed height instead of "seeing" a change from "auto" directly to 0,
   which does not get animated

Simplify the API of `MenuItem` a little by passing the content of the
submenu directly rather than a function to render the submenu. The
downside of this is that `MenuItem` cannot skip rendering the submenu
content when the submenu is not visible, but the implementation does not
do this anyway.

To ensure consistency between different menus that contain items with
submenus, move the responsibility for rendering the submenu and its
container to the `MenuItem` component. The component that renders the
top-level `MenuItem` must supply a `renderSubmenu` prop that renders the
submenu on-demand.

It seems to me like the expanded submenu should be treated as ephemeral
state which is lost/reset when the menu is closed.

Replace the per-GroupListItem state indicating whether the item's submenu is
open with a per-GroupList state variable indicating which group (or none) has
its submenu currently expanded.

This transition is not as simple as applying a CSS transition
property to an element since browsers do not support animating `width`
/ `height` from 0px to "auto" to fit the content. Therefore add a
component to handle the steps in the transition.

Move real-time update state to store

Convert new-note-btn to preact

Convert search status bar to preact

Merge pull request #1262 from hypothesis/dependabot/npm_and_yarn/karma-coverage-istanbul-reporter-2.0.6

Bump karma-coverage-istanbul-reporter from 2.0.5 to 2.0.6

Bump karma-browserify from 6.0.0 to 6.1.0

Bump @babel/preset-env from 7.5.4 to 7.5.5

Bump enzyme-adapter-preact-pure from 2.0.0 to 2.0.1

Update ESLint configuration

Bump @octokit/rest from 16.28.4 to 16.28.5

Bumps [@babel/preset-env](https://github.com/babel/babel) from 7.5.4 to 7.5.5.
- [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/v7.5.4...v7.5.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump babel-plugin-istanbul from 5.1.4 to 5.2.0

Bumps [karma-browserify](https://github.com/nikku/karma-browserify) from 6.0.0 to 6.1.0.
- [Release notes](https://github.com/nikku/karma-browserify/releases)
- [Commits](https://github.com/nikku/karma-browserify/compare/v6.0.0...v6.1.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump gulp-if from 2.0.2 to 3.0.0

Bump mocha from 6.1.4 to 6.2.0

Bump @babel/core from 7.5.4 to 7.5.5

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 16.28.4 to 16.28.5.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v16.28.4...v16.28.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [enzyme-adapter-preact-pure](https://github.com/preactjs/enzyme-adapter-preact-pure) from 2.0.0 to 2.0.1.
- [Release notes](https://github.com/preactjs/enzyme-adapter-preact-pure/releases)
- [Changelog](https://github.com/preactjs/enzyme-adapter-preact-pure/blob/master/CHANGELOG.md)
- [Commits](https://github.com/preactjs/enzyme-adapter-preact-pure/compare/v2.0.0...v2.0.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [karma-coverage-istanbul-reporter](https://github.com/mattlewis92/karma-coverage-istanbul-reporter) from 2.0.5 to 2.0.6.
- [Release notes](https://github.com/mattlewis92/karma-coverage-istanbul-reporter/releases)
- [Changelog](https://github.com/mattlewis92/karma-coverage-istanbul-reporter/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mattlewis92/karma-coverage-istanbul-reporter/compare/v2.0.5...v2.0.6)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [babel-plugin-istanbul](https://github.com/istanbuljs/babel-plugin-istanbul) from 5.1.4 to 5.2.0.
- [Release notes](https://github.com/istanbuljs/babel-plugin-istanbul/releases)
- [Changelog](https://github.com/istanbuljs/babel-plugin-istanbul/blob/master/CHANGELOG.md)
- [Commits](https://github.com/istanbuljs/babel-plugin-istanbul/compare/v5.1.4...v5.2.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [gulp-if](https://github.com/robrich/gulp-if) from 2.0.2 to 3.0.0.
- [Release notes](https://github.com/robrich/gulp-if/releases)
- [Commits](https://github.com/robrich/gulp-if/compare/2.0.2...3.0.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [mocha](https://github.com/mochajs/mocha) from 6.1.4 to 6.2.0.
- [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/v6.1.4...v6.2.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@babel/core](https://github.com/babel/babel) from 7.5.4 to 7.5.5.
- [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/v7.5.4...v7.5.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

 - Add missing `addPendingUpdates` call. The test was previously not
   checking what it was supposed to check
 - Improve a test for the `pendingUpdateCount` selector