fixed some serialization issues regarding PlaylisteEntries and Songs and added some missing specs
fixed an issue with serializing/deserializing ojects which inherit from MediaModelBase
fixed failing spec
removed duplicate event subscription
removed duplicate code The navigation service was set in both a property and a field
added some checks to fix some possible crashes with no descriptive error information
added the DeletePlaylist result
minor code refactoring
modified the way the bottom bar view model is set for collection view models
added the playlist bottombar viewmodel and added the delete functionality to the ManagePlaylistsViewModel
added the SavePlaylistViewModel and implemented saving new playlists