Extract sort dropdown into own component

Extension badge refactor

Extract the sort dropdown into a reusable component
and add tests.

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Make BrowserAction actually stateless - its responsibility
is just to map the logical H state of a tab (active/inactive/errored,
annotation count) to the badge state.

 * Convert the per-tab state stored in TabState from
   a string into an object so that we can store additional
   state, starting with the badge count.

 * Move the function for fetching the badge's annotation
   count and updating the H tab state into TabState.

   This decouples the presentation of the badge from
   the logic of making network requests and updating
   the model.

Update npm / python modules before running tests

Fix an issue where clicking the search icon would submit the form

Make settings loader CSP-compatible

I forgot about CSP! We disallow inline scripts in the Chrome extension,
so 18c47ba broke the extension. This commit replaces an inline script
with some JSON data, parsed by the settings factory.

Clicking the search icon should only focus the search field,
not submit the search.

This addresses the issue mentioned at https://github.com/hypothesis/h/pull/2622#issuecomment-148808509

New design for top bar

Add userid_domain config setting

Fix group link not being focused in dropdown menu if group hash IDs started with a number

The hash ID was not quoted when constructing the selector
used to find the group's link field in order to focus it,
resulting in an error depending on the chars in the hash ID.

Revert "Use "should" instead of "must" for search queries"

Add authors to RSS feed

Simplify streamer

Override the browser default styling on the search
input's width property so that its maximum
width will be limited by the available space
in the top bar when expanded. Previously it
was inflexible due to the browser default styling
with the group name being pushed off the left side
of the top bar as a result.

There is still an issue at the moment in Firefox
where the share icon gets covered by the search bar
when expanded.

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When the top-bar is used in the stream, the content
needs to be centered above the stream's contents.

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 * Add a couple of missing titles

 * Fix hover state for share icon when groups is disabled

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The input field has no padding by default
so that it does not take up space when collapsed.

When expanded we need some padding between the icon
and the input.

53bd01169cd8eb00748f953a6b2488f09637b32c incorrectly
changed the '.annotator-no-transition' selector which disables
the animated width transitions on the sidebar during
manual resizes to '.annotator-frame .annotator-no-transition' which meant
that it did not take effect.

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 * Make the spacing between the top bar icons consistent

 * Remove redundant CSS from top-bar.scss

The CSS usage here is a little ugly because .top-bar__btn
is used inside the <simple-search> directive but at least it
is clear where the style comes from.

This adds updated icons which were designed
together and line up correctly.

Support redirect-after-login

Implement the design changes from https://trello.com/c/DZEDxU4C/90-top-bar-ui-updates

 - Move the 'My Annotations' item up and change the label
   to the account username
 - Swap Feedback and Help
 - Make the 'Sign out' link more subtle

 * BEM-ify the dropdown menu link CSS for consistency
   and to avoid specificity conflicts

Following UX discussion:

 * Expand the search bar only on click rather than hover

 * Add missing title to search bar component

 * Adjust the styling of the icon so that the bottom of
   the 'chat heads' icon for groups is aligned vertically
   with the baseline of the group name label

 * Remove extra space between group name label and dropdown
   indicator arrow

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streamer: Don't silently stop processing on exceptions

Increase top bar height to 40px to match the designs.
A visual side effect is that the dropdown menus now
overlap the top bar and clearly appear on top of it
rather than just below.

Position the arrow at the top of the groups list
dropdown menu so that it appears beneath the
dropdown indicator in the top-bar.

This is done by hiding the dropdown menu's "built in"
arrow created via CSS :before and :after pseudo-elements
and introducing a separate element which uses the same
technique with borders to create the dropdown arrow.

The use of a separate element for the arrow allows it
to be aligned with the right edge of the dropdown menu's
parent element (in this case, the group name in the top bar)
rather than the dropdown menu's content.

 * Set the inner container in the top bar to the full height
   of the top bar.

   This corrects the vertical alignment of the toolbar icons.

 * Remove the extraneous 'content' class from the top bar

 * Remove unused selectors for button styling

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When the new top-bar design is enabled,
collapse the search input unless the field is hovered,
focused or there is an active search query.

In the legacy top-bar design, the search field remains
expanded all the time

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Explicit settings for websocket

Rather than constructing a URL from hard-coded defaults in the streamer
service, we pass the websocket URL from the backend in the settings
object and use this when opening the websocket.

The approach of embedding a link tag in the app.html doesn't really give
us a great deal of flexibility. URLs within the application, perhaps as
a result, tend to be created either from baseURI or from the API URL,
called `serviceUrl` in the code.

This commit leaves the <base> tag alone, but:

- replaces the serviceUrl <link> tag with a settings object,
  `window.hypothesis.settings` which is inlined into app.html.
- replaces the serviceUrl angular service with a generic settings
  service.
- renames serviceUrl to apiUrl, to make its purpose more obvious.

Update the button styling for top bar icons to match
the mocks.

The icons have been changed to <a> rather than <button> tags
to work around an issue I see in Firefox where the icon
is initially clipped when loaded and then re-renders itself
correctly on hover. This needs additional investigation.

 * Make the corners of the top bar straight

 * Remove the unnecessary border at the top of the sidebar,
   since the sidebar is already bordered by the bottom
   of the browser's address bar

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Variables in calc() expressions must be interpolated.

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