Refactor MediaElement Controls VideoModel -> PlaybackController

[dsparacio]

Currently we partially implement video element API layer ( play, pause, seek time duration etc... ) in MediaPlayer and this was done for DVR window capabilities. Need to fully implement so a user can just call API and listen to events with one object, MediaPlayer.

Once I started looking at the code I notice we have partial element control in two places internally. I understand why we need to be able to control the element internally but we need to clean this up.

Solution..
Refactor the duplicated / parallel code in VideoModel into PlaybackController as well as add the missing Video Element API layer desired and map all calls to video element in mediaplayer to this controller.

[dsparacio]

Fixed with PR #1020