Remove empty categories from the section view.
Merge pull request #118 from hudl/Section_RemoveEmptyGroups

Remove empty categories from the section view.
Merge branch 'UI_Overhaul' of github.com:hudl/hudl-win8 into Caching
Fixed bug where when a new user logs in on the same device, it displays previous user's video by clearing the cache when the user logs out.