Extract `quote` function from annotation / view-filter

Both `components/annotation` and `view-filter` modules had logic and
tests for extracting a quote from an annotation object. Extract these
into a shared `quote` function in `util/annotation-metadata`.

One small change is that `view-filter`'s implementation allowed
annotation objects with _no_ `target` property. These should never
occur. There is a known issue where creating a Page Note results in an
annotation with an _empty_ `target` property until the annotation is
saved (see [1]). That case, which is still handled, looks like a mistake,
but resolving it is outside the scope of this change.

[1] https://github.com/hypothesis/client/issues/1290

Fix module load error on pages defining `require`

There are two expressions which reference a global `require` function in
the Browserify prelude. Both of them need to be rewritten to use
`hypothesisRequire` instead. Previously only the first use was
rewritten, which worked as long as the page didn't define its own
`require` function. On https://qa.hypothes.is/search for example, h's
JavaScript bundles do.

Refactor `AnnotationBody` and `AnnotationQuote` styles

Update annotation icons (footer icons) to newer, SVG variants

Improve minification of JS bundles

Bump autoprefixer from 9.7.2 to 9.7.3

Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 9.7.2 to 9.7.3.
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/autoprefixer/compare/9.7.2...9.7.3)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [eslint-plugin-react](https://github.com/yannickcr/eslint-plugin-react) from 7.16.0 to 7.17.0.
- [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/v7.16.0...v7.17.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.578.0 to 2.581.0.
- [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/v2.578.0...v2.581.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [eslint](https://github.com/eslint/eslint) from 6.7.1 to 6.7.2.
- [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/v6.7.1...v6.7.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

 - Move the styles for these components out of `annotation.scss` and into
   separate files to follow project conventions.

 - Refactor style names to use BEM-ish naming conventions

There are some exceptions here because annotation body and quote
elements have styles that are customized when the annotation is a reply
or when the annotation card is hovered. Those customizations are still
in annotation.scss because they need to match both the parent and child
components.

Remove the `hasContent` prop because it can be inferred by looking at
the `text` prop instead. If an annotation has been moderated, then the
`text` will either be non-empty if the user is a moderator or it will be
redacted and thus be empty if the user is not a moderator.

Make it easier to test a production build of the client locally by
making `env NODE_ENV=production gulp watch` build code with production
JS/CSS transforms applied but still load assets from the dev server
instead of from https://cdn.hypothes.is.

Add a flag to the function that builds the boot script indicating whether we
are running the dev server, and take that into account when determining the
asset path.

When building the bundle, wait for the final stream to finish writing
output, rather than the intermediate stream.

In order to avoid conflicts with any existing global `require` functions
on the host page, JS bundles are configured to export their `require`
function as `hypothesisRequire` and bundles loader later are modified to
use that function to import modules from earlier bundles.

Overriding the name used for importing from earlier bundles was
previously done by prepending some code to the start of the bundle.
Unfortunately the source map information was not updated so this broke
sourcemap locations in the generated bundle.

Change the approach instead to modify the "prelude" script that
Browserify inserts at the top of the bundle.

When minifying code with terser, make sure the existing sourcemaps for
the input code are taken into account.

Previously only the _contents_ of modules were minified, but not the
module infrastructure that Browserify adds around it. Given lots of modules,
this adds up.

Replace `uglifify` with a small wrapper around terser, the package that
actually compresses the code, and use it to minify both the contents of
modules and the generated wrapper code. Calling terser directly allows
us to a) use the current version of it (uglifyify was stuck on Terser
3.x) and b) upgrade/configure/replace it more directly in future.

One other change here is that minifying modules is now done _after_ the
transform that replaces `if (process.env.NODE_ENV == ...)` checks with
`if (true)` or `if (false)`. This enables dead-code removal to remove
the logic entirely.

This reduces the minified size of `sidebar.bundle.js` from 368 KB to 311
KB (-15%) and `annotator.bundle.js` from 170 KB to 152 KB (-12.7%).
Some vendor bundles are smaller, others are unaffected because they were
already fully minified. The total minified size of all bundles is reduced by ~7%.

Remove unused Angular annotation-share template

Make simple fix to `AnnotationShareControl` to suppress errors on logout

Add a quick fix so that users will not see an error on logout when there
is a temporary state of the app during which the `group` prop may be
undefined.

Part of https://github.com/hypothesis/client/issues/1542

Revert "Improve compression of JavaScript bundles"

Fix cause of flakiness in `observeElementSize` test

Improve compression of JavaScript bundles

Update annotation action icons to updated variants, adjust
CSS for improved layout and interaction; increase tap-target
size for mobile users.

Replace `share-annotation-dialog` with preact `AnnotationShareControl`

Add preact component for sharing a single annotation. Replace use of
`share-annotation-dialog` within the `annotation` component with this
new component.

Bump @sentry/browser from 5.9.0 to 5.9.1

 - Wait for a specific event, the observer callback being called, when
   possible. This avoids a possible issue where
   `ResizeObserver`/`MutationObserver` callbacks would not be delivered
   within the fixed time
 - Fix a typo in the name of the test file

Original issue report: https://hypothes-is.slack.com/archives/C1M8NH76X/p1574692275043700

Bump autoprefixer from 9.7.1 to 9.7.2

Bump sass from 1.23.6 to 1.23.7