Hotfix/release multiple video bug

Hotfix/xml parsing

Check extension rather than mimetype

Comments (and processing instructions!) are handled oddly in lxml.
This change will keep them from causing failures.  They will be omitted
from the HTML generated, which is fine, since they aren't needed there.

   Contains hotfix/2013-18-21

Fix/vik/oe state

Video Player: replace the description in the studio editing module for "subtitles" with "timed transcript"

Adam/turn off password autocomplete

Add combined coverage to `rake coverage`

Change `rake pep8` to ignore migrations files

fix error logging for unenrolling if enrollment not found

Add a python prefix for `diff-quality` task

Jkarni/feature/chunkedupload

Signed-off-by: Julian Arni <julian@edx.org>

  Comments, httpresponse -> jsonresponse; make sure errors get relayed.

   Also adds lockfile for asynchronous status updates.

Bug fix -- subcategories in forums topic list should now be sorted alphabetically