Refactor checklinks command

* Create model to track Video URL statuses, add migrations and tests.
* Pull some of the checklinks.py functions into the new models

Conflicts:
	richard/videos/management/commands/checklinks.py
Sync up travis with tox config

Queue up the headesk bashing! I'm off to battle Travis again!
Tweak output of checklinks command

This just makes it show more information when it's in verbose 2.