return MovieCell for all other cells where we don't have yet a designated cell

When you add a childViewConroller to a UITabbarcontroller it will keep them in the viewControllers.
by setting the viewControllers on the tabbarcontroller later we removed the childViewController which led to that Controller
not getting any updates like willTransitionToSize. Simply appending the other viewcontrollers would show the player as additional tab
We now have plain UiViewController with tabbarController and PlayerController as ChildViewControllers to fix this layout issue

(closes #292)

This allows monitoring of changes in the Documents folder from external
apps.

Additionally changes `mediaFilesFoundRequiringAdditionToStorageBackend`
to optional since the new medialibrary doesn't need it.

(closes #297)

and capitalize string

if an external screen is connected we're not showing the tracklabel anymore but display
that information as part of the external views title (closes ##222)

- This removes the old playlistTableviewcell and Collectionviewcell
- it puts in place the architecture for further cells by adding a baseCollectionViewCell

* position indicator in the middle of the movieViewController
* simplify state code and only show the indicator for buffering when we are not in paused mode before
since we never get an event that we're done with buffering (closes #306)

(cherry picked from commit 58fcf383)

The presentedViewController in that case is nil and therefore nothing is displayed

(cherry picked from commit 19c863d2)

(closes #269)

(closes #293)

(closes #294)

(closes #240)