Don't allow "Hide Closed" to bleed into dashboard datagrids.

The toggle for hiding closed review requests on the user and all review request
grids would set a profile flag, and then bled into the "All Outgoing" datagrid.
This change adds some plumbing to prevent this from happening.

Testing done:
Reproduced the bug, and then tried with this change. Saw that with the profile
flag set, the dashboard datagrids showed closed review requests, but the others
did not.

Fixes bug 3319.

Reviewed at https://reviews.reviewboard.org/r/5746/
Normalize filediff filenames during creation.

Some of the diff APIs that we're using for post-commit review request creation
(looking at you, GitHub) give us filenames with leading slashes. This doesn't
match what we have elsewhere, which makes things annoying if filenames don't
match.

Testing done:
Used this in conjunction with testing out the suggested reviewers feature. Saw
that when I created a post-commit review request, the filenames matched what
would have been created from rbtools.

Reviewed at https://reviews.reviewboard.org/r/5734/
Switch to more explicit CSS styles for boxes in Review Board.

Boxes in Review Board now follow the new convention in Djblets of
prefixing all related CSS classes with "box-" and wrapping the title
element in a "box-head" div.

This matches what we've been using in RBCommons, helping us to keep
things consistent, and prevents conflicts with existing "title" and
"main" CSS classes.

Reviewed at https://reviews.reviewboard.org/r/5754/