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/