updates module, with tests, sans UI (will extract from video_download
adding comments, removing cruft, a small code switch for safety.
Merge branch 'checkconnection' of github.com:bcipolli/ka-lite into updates_app

Conflicts:
	kalite/main/api_views.py
	kalite/settings.py
secondary checkin; most of the functionality is there.
cleanup of interactions (just missing a 'waiting to begin' message)
pointing subtitles client at ourselves.
hardcoding playground
Merge branch 'develop' of github.com:learningequality/ka-lite into subtitles_from_FLE
Merge branch 'subtitles_from_FLE' into updates_app
initial checkin--videos mostly working, subtitles broken, updates landing page working, update software broken.
extending BaseCommand to know how to use the UpdateProgressLog object, then making videocommand use that interface.
Expose endpoints for downloading KA Lite
Merge branch 'updates_app' of github.com:bcipolli/ka-lite into update_all
Merge branch 'download_kalite' of github.com:bcipolli/ka-lite into update_all
adding 'static' update command type
Merge branch 'updates_app' into update_all
making update use updates table.
basic update page working, with failsafe...
move as much installation logic to python as possible.
migrate from print/sys.exit to stdout/CommandError. Get database path programmatically. Configure permissions for apache in apache config script.