added the ability to display a video in fullscreen mode
modified the StartVideoPlaybackMessage, FullScreenVideoPlaybackViewModel nad PlaybackViewModel so that a user can switch between fullscreen mode while remaining at the same position in the video
extracted the VideoPlaybackViewModel class and made the FullScreenVideoPlaybackViewModel and the new EmbededVideoPlaybackViewModel classes inherit from this class to separate logic and reduce code duplication
fixed a bug leftover from refactorings
fixed an issue with the content of the video view disappearing when going back to the playback view
modified the playlistmanagement service so that the default behavior for play video file is to play it in fullscreen
fixed a possible issue with timespan arithmetics
Merge pull request #38 from cristi-badila/fullScreenAbility

Full screen ability