merging current and release-0.11 video update code
Small output tweaks
Fixing up the computation of percent complete
Cleaning out subtitles stuff, making delete really work (was having issues with delete, then download), removing duplicated code.
Making sure that when a job ends, the corresponding UpdateProgressLog gets closed too.
Making generic progress tracking run more smoothly.
Making video updates run more smoothly.
Styling and wording tweaks on easy admin page.
Merge branch 'release-0.11' of github.com:learningequality/ka-lite into video-update-update

Conflicts:
	kalite/templates/updates/update_videos.html
	kalite/updates/api_views.py
Better error reporting, showing actual # of videos being downloaded, fix a couple of small bugs.  Ready to go!
Merge branch 'video-update-update' of github.com:bcipolli/ka-lite into allow-mem-cache
Move all cache invalidation into create/delete signals on VideoFile objects
Migrating back to bulk_create, and using property update of percent_complete=100 to trigger cache invalidation
Merge branch 'master' of github.com:learningequality/ka-lite into release-central
Adding custom validation
Fixes both issues in #880; styling issue due to missing </div> closing tag.
Change wording of subscribe checkbox
checking box by default
Remove trans tag from JS file string.
Give "cancel" button some breathing room above it on update page.