Merge pull request #1 from mcharite/develop

Develop
Merge pull request #2 from mcharite/feature/UnitTestDBManager

Feature/unit test db manager
Merge pull request #3 from mcharite/develop

Develop
setting up artist relationship with content
removed the default value of null for RLMObject instances in model classes
established relationship of tracks to artist
established relationship between Mixtape and Artist
fixed database relationship between Video and Artist
removed NSLog from TracksTVC