Simplify root thread generation in top-level UI components

Bump eslint-plugin-react from 7.14.2 to 7.14.3

Merge pull request #1274 from hypothesis/dependabot/npm_and_yarn/karma-coverage-istanbul-reporter-2.1.0

Bump karma-coverage-istanbul-reporter from 2.0.6 to 2.1.0

Bump @octokit/rest from 16.28.5 to 16.28.7

Merge pull request #1278 from hypothesis/dependabot/npm_and_yarn/babel-plugin-transform-async-to-promises-0.8.13

Bump babel-plugin-transform-async-to-promises from 0.8.12 to 0.8.13

Fix typo `bnt` -> `btn` in `SelectionTabs` component

Bumps [babel-plugin-transform-async-to-promises](https://github.com/rpetrich/babel-plugin-transform-async-to-promises) from 0.8.12 to 0.8.13.
- [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/v0.8.12...v0.8.13)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [eslint-plugin-react](https://github.com/yannickcr/eslint-plugin-react) from 7.14.2 to 7.14.3.
- [Release notes](https://github.com/yannickcr/eslint-plugin-react/releases)
- [Changelog](https://github.com/yannickcr/eslint-plugin-react/blob/master/CHANGELOG.md)
- [Commits](https://github.com/yannickcr/eslint-plugin-react/compare/v7.14.2...v7.14.3)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 16.28.5 to 16.28.7.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v16.28.5...v16.28.7)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [karma-coverage-istanbul-reporter](https://github.com/mattlewis92/karma-coverage-istanbul-reporter) from 2.0.6 to 2.1.0.
- [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/v2.0.6...v2.1.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Since an Angular digest cycle is triggered whenever Redux store state
changes, we can simplify the top-level component controllers in the UI
by making `vm.rootThread` a method which generates the top-level thread
when called.

Since `rootThread.thread` memoizes based its input, thread recalculation
won't happen more often than necessary.

This change should also make it easier to migrate these components to
Preact/React in future.

Move tab counts to store

Previously, the number of annotations in each tab and the currently
selected tab were passed from the sidebar into the search-status-bar
and selection-tab components. Now, they are  grabbed from the store.

Remove unused ng component wrappers

The only consumers of these components have been converted to Preact

This component has been migrated to Preact

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