Redid set_video_id as data migration, using orm references, not imports
Add CronCommand - a command that can only be run from the command-line.  Why you'd want this: to interact with chronograph easily, but to force the command to be run within the server process.
Get youtube-dl working with callbacks.
Fix for #1455: don't retry non-connection errors
Moved fixed migration code to a new 0029, and made 0028 into a dummy.

(as the old 0028 had already been shipped)
Fix for #1662: re-apply KA-LITE-MOD to khan-exercises
add missing qtip2 css, cleanup
Merge pull request #1645 from jamalex/set_video_id_migration

Redid set_video_id as data migration, using orm references, not imports
Adding comment to i18n/__init__.py, to try and warn against breaking main migrations.
Merge pull request #1666 from bcipolli/1662

Fix for #1662: re-apply KA-LITE-MOD to khan-exercises
Merge pull request #1667 from mauk81/develop

add missing qtip2 css
Change default debug central server host
Merge pull request #1650 from bcipolli/1455

Don't retry non-connectivity errors... and implementing iterative download updates for youtube-dl
Merge branch 'develop' of github.com:learningequality/ka-lite into 1477

Conflicts:
	kalite/updates/management/commands/videodownload.py
remove auto-pdb from automatically added args when DEBUG = True
Merge pull request #1648 from bcipolli/1477

Add CronCommand - a command that can only be run from the command-line.