Move static media to static/ and start compiling it.

Until now, static media has lived in djblets/media, which didn't match all of
our other codebases. I've moved all the files to djblets/static and set things
up to compile together our various javascript and CSS files.

As part of this, we no longer ship our own copies of jquery and jquery-ui.
The templates now load these from the google CDN.

Testing done:
* Ran build-media.py and verified that everything got compiled correctly.
* Used this from Review Board and tested that the dashboard and extensions
  pages still worked and looked correct.

Reviewed at https://reviews.reviewboard.org/r/4654/
Move to LessCSS and nest our existing styles.

This moves the djblets CSS to use Less instead of plain CSS. I've done some
nominal cleanup to nest the existing rules, but there's plenty more (especially
with naming/computing our colors) that can be done.

Testing done: Verified the appearance of the dashboard and extension list.
Reviewed at https://reviews.reviewboard.org/r/4673/
Convert datagrids to use a spritesheet for icons and add retina support.

This change moves the artwork for the datagrids into a spritesheet which is
rendered at both 1x and 2x resolution. This works in a very similar way to the
Review Board artwork.

Testing done:
Checked the appearance of all the new icons on both low-dpi and high-dpi
screens.

Reviewed at https://reviews.reviewboard.org/r/4672/
Break apart jquery.gravy.js into a bunch of component pieces.

Some of this stuff (especially in hacks) is probably obsolete, but I didn't
want to get too much into making substantive changes. The only actual changes
to the code are:
* Changing jQuery to $
* Fixing some random issues that jshint pointed out (mostly missing
  semicolons).

Testing done:
Smoke tested modal box, inline editor, and other js functionality.

Reviewed at https://reviews.reviewboard.org/r/4676/
Set the tracking branch for this branch.
Merge branch 'release-0.7.x'