Fix for Video.get_video_url()
Made entry parsing work on the initial import

We have 2 ways to import videos into from a feed: the
tasks.import_videos_from_feeds() method and VideoFeed.update().  Both
of them basically did the same thing, but with duplicate code.  I only
updated the VideoFeed.update() method, so the initial import wasn't
picking up the titles.

Refactored things so that the importer code is in
feed_parser.VideoImporter.

Refactored the video feed tests and added a teams feed test.
Fixed exception after we finished the import task