This moves away from measuring layout of non-typographical elements
in ems, favoring px for better consistency across devices with different
pixel densities. While that may sound backward, the reality is that CSS
pixels are device independent, and non-integer em values seem to be handled
less consistently.

Finally, there were some font size and line height tweaks made here to match
the new measurements of the top bar. This provides a consistent feel to the
top bar across devices and dpi.

Added loading icon suggestion and basic CSS.

Added contributing information and useful resources to the homepage.

Changed icons to give them a consistent style.

Changed positioning on topbar to fixed on the streams page. It's much more consistent with design on feed-type sites like Facebook and Twitter.

See #1020 for a description of the problem.

This commit patches the merge behavior of the bridge plugin:
never update a list of targets with a shorter list.
(This avoids it being zeroed by accident.)

This does not really solve the more generic problem: the race condition
of the messages moving on the bridge. We should either do some
time-stamping, or some other smarter flow control...

Fix #575

Changed how threading works.

Conflicts:
	h/js/services.coffee

Updated Annotator TextHighlights plugin to  c90ac7cd (typed packaging branch), with performance improvements

Fixes #972

Fixed bug where the wrong icon would show marking an annotation as private. 

Because of that many load top annotation labels were missing.

Fixes #948

After login/logout if there were search results, they were not displayed again. Now a new event is broadcasted to which the SearchController listens to and calls the refresh() again.
Currently it is done with a timer. The most elegant solution would be having an event about loading and anchoring all annotations and after that we could call this event properly.

Fixes #959

Made a slight mistake in my Iconwork PR. This fixes it. On private annotations the wrong icon was showing.

Updated icons for toolbar. Cleaned up Icomoon session file to reduce its size.

Updated icons for toolbar. Cleaned up Icomoon session file to reduce its size and bring it up to date with the newest version of the Icomoon app.

 * Updated dom-text-mapper to 3fb30bee (master branch)
 * Updated Annotator to 631c1345 (typed-packaging branch)

These are all internal DTM / Annotator changes.
The communcation about DOM changes has migrated from method calls
to events.

See also https://github.com/hypothesis/dom-text-mapper/issues/14

When hovering the mouse over a visible highlight, add a drop shadow to the annotation card in the sidebar.

Fixes #918.
Also fixes #957.