Remove an old comment about Repository path:local_site constraints.

We had an old comment describing how a path:local_site unique constraint
was causing problems when archiving repositories. This was an issue
because an archived repository would keep the path, but wouldn't be
shown in the UI, resulting in a conflict when trying to add a new
repository with the same path.

We fixed this in 2.0 by including an archive timestamp in the key. The
comment hasn't been relevant for a while now, so we can safely delete
it.
Fix generating the path to the manual URL for dev builds.

The old manual URL generation function was assuming that any
non-released builds should us the 'dev' docs, but this is often wrong.
What we actually want is to use the 'dev' docs for any X.Y.0 releases
that aren't marked as "final". This changes the logic accordingly.

Reviewed at https://reviews.reviewboard.org/r/6579/
Sandbox reviewboard.attachments.mimetypes.MimetypeHandler

Extensions that create a MimetypeHandler subclass can throw exceptions inside
Review Board. The sections of Review Board that call those methods have been
sandboxed.

Now when a MimetypeHandler subclass from an extension throws an exception,
Review Board logs the errors. The error logs give enough information to find
which method in the MimetypeHandler subclass threw the exception.

Testing Done:
Unit tests have been written to make sure that functions from an
MimetypeHandler subclass have been called, and when an exception is thrown it
gets logged.

The tests fail without the sandboxing, and succeed with it.

Reviewed at https://reviews.reviewboard.org/r/6532/
Refactor the alphabetic paginator.

This updates Review Board for the associated Djblets change to refactor the
alphabetic paginator into a subclass.

Testing Done:
- Unit tests all pass
- All button cases manually tested. (Forward, back, first and last arrows, each
  letter).
- Verified that  changes to not affect any other module that inherits from
  datagrid (such as the groups list, or the all review requests list, the
  current 'master' of reviewboard with no changes to the userGrid).

Bugs closed: 829

Reviewed at https://reviews.reviewboard.org/r/6522/
Fix multi-select closing in the dashboard for Local Sites.

The multi-select closing in the dashboard wasn't providing any local
site information, and wasn't using the display ID for review requests.
We now pass the proper information to the template and JavaScript in
order to handle this case.

Reviewed at https://reviews.reviewboard.org/r/6588/
Fixes bug #3561
Merge branch 'release-2.0.x'