Adds stickybuttons to the toolbar.

Fixes #831.

Since I can't think of a way to reset specifically to the browser
default font size we'll have to just set the font size explicitly.

Fixes #822

Fixes #820

Fixes #819

This should ensure that after a user decides not to log in their
ongoing edits or highlight switches are cancelled and any partially
entered login details are cleared.

This is so that an ongoing edit does not become a draft until login
is completed. Otherwise, we leak drafts when the login pop-up is
ignored.

On $reset event, authentication model fields weren't being cleared.

- Wait until we have a token to finish on-going edits
- Make sure to reset the on-going highlight switch
- No need to cancel on route change now that draft discarding does that

Prevents losing track of drafts when switching from highlighter to
comment tool if replies have been started in the sidebar.

Refactored the way changing the tool triggers setting visible highlights.
The change should always ensure better interaction if other components
change the tool or highlight state in the future and trigger events.

For #798

For #798

This change may affect #803 and #805.

I believe this is no longer necessary since we started using
`event.preventDefault` more consistently in annotation actions.

That's good, because this timeout stuff was brittle.

Previously, we were adding fake highlights to comments, which
showed up on the last character of the document, when in always-on
or highlight mode.

This was needed so that the heatmap can find the comments.

The new implementatain is much cleaner; now we maintain a list of comments
independently of the DOM, and the heatmap works from that.

Therefore, the fake highlights are now gone.

Fixes #700.

Update INSTALL.OSX.rst

Bridge: don't skip old data in the 'loadAnnotations' notifications

Previously the fuzzyTime filter showed fuzzy value for dates no older than 30 days. After that it just displayed an unformatted new Date(date) which looks strange compared to the other displayed time strings.
Now it has been extended to show x. month ago and y years ago.

Fixes #799

Earlier when a 'loadAnnotations' notification was sent on the bridge plugin,
 * Only locally created annotations were included; annotations with
   existing bridge tags were never sent. This was true even if the
   'annotationsLoaded` event (which we are reacting to) contained such
   annotations.
 * On the receiving end, existing annotations were dropped without being
   parsed.

This made it impossible to propagate data via this notification.
However, when we do the actual anchoring in the host document, we are
trying to use this notification to spread the data which become available
as the result of the anchoring; for example, the visual diffs.

To fix this, I have made the following changes:
 * All annotations (coming from the 'annotationsLoaded' event are sent
   with the notifications
 * On the receiving end, all annotations are parsed, so that the updates
   in various fields can be merged in. Of course the already existing
   annotations are not included in the subsequent `loadAnnotations()` call.

This fixes #807.