Improved sync history admin form. (#1495)

I made a bunch of fields read-only.  This avoids the performance hit
that janet was talking about and I think it keeps the form sane.  The
only things I can see an admin changing are the status and the details
text.
Name change for the external sites settings tab (#1486)
Update django to the newest release
Merge pull request #1506 from pculture/brightcove

Brightcove
Merge pull request #1496 from pculture/django-1.4.13

Update django to the newest release - great!
Merge pull request #1497 from pculture/gh-1486

Name change for the external sites settings tab (#1486)
Merge pull request #1498 from pculture/gh-1495

Improved sync history admin form. (#1495)
Use SubtitleLoader to load our subtitles

This method allows us to store the styling/layout data in the amara
repo instead of a string in the babelsubs repo.  I also switched the
styles to use the suggested ones from #1012.

Also changed the DFXP that we create for new subtitles in the
javascript editor.