Previously video embeds were given a fixed with of 369px, which is close
to the width available to annotation content at the sidebar's default width
(~380px). On narrower viewports the video would get cut off.

Fix this by setting the width of video embeds to `100%` and using a CSS
hack [1] to set the height of the video such that the embed has a 16:9
aspect ratio, which is what YouTube optimizes for.

 - Set `width: 100%` on `excerpt__content` and `markdown-view` so that
   the annotation content always fills the available width.

 - Add support for specifying a class name for embed containers when
   calling `replaceLinksWithEmbeds` and use that to give embeds rendered
   in `MarkdownView` a `width` of 100%.

 - Change `replaceLinksWithEmbeds` to wrap iframes with an aspect-ratio
   box (see [1]) which causes the iframe's height to be adjusted as the
   width changes to have a 16:9 aspect ratio.

   Adding this container required changes in `media-embedder-test` to
   allow the `<iframe>` to be wrapped in a container element.

[1] https://css-tricks.com/aspect-ratio-boxes/

- TagList
- TagEditor
- MarkdownEditor
- Excerpt
- AutocompleteList
- AnnotationBody

Add SidebarStore type. This is an aggregation of the base ReduxStore + each one of our stores baked in. The fist store added here is simply the Activity store (as a first example)

There are some assumptions when making store types:

1. It is assumed they are transformed in `createStore` where the selectors and actions are flattened.

2. Some meta data (namely, the init method, namespace and update method) are refactored or removed.

These transformations are implied through the typing which explicitly ignores these methods and structure of the raw store before the transformation in create-store.

Bump codecov from 3.7.0 to 3.7.1

Convert store selectors to receive local rather than root state

Since selectors are attached to the `store` as methods, selectors from
different modules are not allowed to have the same name.

Make a clear distinction from variables which hold module-local state,
called `state` elsewhere in the file.

Bumps [codecov](https://github.com/codecov/codecov-node) from 3.7.0 to 3.7.1.
- [Release notes](https://github.com/codecov/codecov-node/releases)
- [Commits](https://github.com/codecov/codecov-node/compare/v3.7.0...v3.7.1)
Signed-off-by: dependabot[bot] <support@github.com>

Change store module selectors to receive the module's local state rather than
the global/root state as the first argument. The majority of selectors only need
access to the module's local state. Changing these selectors to receive the
local rather than root state has benefits:

 - It avoids the need for the selectors to know about the structure of
   the root state. This can make future refactorings and re-use easier.

 - It is consistent with how state is accessed in the reducer functions

 - It will simplify typing selectors because the type of the `state`
   argument will be the same as the type of `state` returned by `init`
   and passed to `update` functions

 - It potentially enables automatic memoization of selectors based on
   the local state. ie. If the local state for a module has not changed as a
   result of an action, then none of the local selectors will need to be
   recomputed

There are a small number of selectors that need access to state from
multple modules. In future we may want to move these to some separate
location but, as an incremental step, add support for "root selectors"
to modules under a `rootSelectors` key. These selectors will still receive the
root state as their first argument as before.

This commit also adds missing tests for the `annotationExists` selector and the
`route` module.

See also https://hypothes-is.slack.com/archives/C1M8NH76X/p1595237570226700.

Bump @sentry/browser from 5.19.1 to 5.19.2

Bump fetch-mock from 9.10.3 to 9.10.4

Bump preact from 10.4.5 to 10.4.6

Bump typescript from 3.9.6 to 3.9.7

[Security] Bump codecov from 3.7.0 to 3.7.1

Bumps [@sentry/browser](https://github.com/getsentry/sentry-javascript) from 5.19.1 to 5.19.2.
- [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/5.19.1...5.19.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 18.0.0 to 18.0.1.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v18.0.0...v18.0.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [eslint](https://github.com/eslint/eslint) from 7.4.0 to 7.5.0.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
- [Commits](https://github.com/eslint/eslint/compare/v7.4.0...v7.5.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.713.0 to 2.715.0.
- [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/v2.713.0...v2.715.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@babel/core](https://github.com/babel/babel/tree/HEAD/packages/babel-core) from 7.10.4 to 7.10.5.
- [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/v7.10.5/packages/babel-core)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [preact](https://github.com/preactjs/preact) from 10.4.5 to 10.4.6.
- [Release notes](https://github.com/preactjs/preact/releases)
- [Commits](https://github.com/preactjs/preact/compare/10.4.5...10.4.6)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [enzyme-adapter-preact-pure](https://github.com/preactjs/enzyme-adapter-preact-pure) from 2.2.0 to 2.2.1.
- [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/v2.2.0...v2.2.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [fetch-mock](https://github.com/wheresrhys/fetch-mock) from 9.10.3 to 9.10.4.
- [Release notes](https://github.com/wheresrhys/fetch-mock/releases)
- [Commits](https://github.com/wheresrhys/fetch-mock/compare/v9.10.3...v9.10.4)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [typescript](https://github.com/Microsoft/TypeScript) from 3.9.6 to 3.9.7.
- [Release notes](https://github.com/Microsoft/TypeScript/releases)
- [Commits](https://github.com/Microsoft/TypeScript/compare/v3.9.6...v3.9.7)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [codecov](https://github.com/codecov/codecov-node) from 3.7.0 to 3.7.1. **This update includes a security fix.**
- [Release notes](https://github.com/codecov/codecov-node/releases)
- [Commits](https://github.com/codecov/codecov-node/compare/v3.7.0...v3.7.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Refactor store annotations tests to use public store API

Do not render the only-me icon while an annotation is being edited, as
the user can switch privacy settings in the editing mode, and those
changes could be at odds with "only me."

Highlight state is relevant on an annotation-by-annotation basis but
does not have any impact on whether an annotation is present or
visible (at all) to the user, which is what `selection` state is for.

At this time, remove highlight-state logic from thread-building as this
is an extra complexity for something that isn't implemented in the UI
anyway.

In future, to re-implement highlight styling, query the `annotations`
store state (perhaps add a `annotationIsHighlighted` selector for
convenience).

The majority of store module tests now work by creating an instance of the
store with a subset of store modules and then using the store's public
methods to manipulate data.

There were some tests for `store/modules/annotations.js` that pre-date
this convention and still called functions exported from the module
directly, passing in `store.getState()`.

Refactor these tests to use the public API for consistency and also to
make future changes to the internal store structure easier.