added: MediaItemTag for ManagedMediaSources.
added: silent track for FailedMediaSource.
added: keyframe fast forward at initial playback buffer.
added: error notification on silently skipped streams.
-Added sync buttons on live streams to allow seeking to live edge.
-Added custom cache key for extractor sources to allow more persistent reuse.
-Refactored player data source factories into own class and separating live and non-live data sources.