Support for initializing player with a parsed manifest

Created by: greg80303

As part of my work to allow the fetching of DRM licenses outside the player, it is necessary to allow the MediaPlayer to be initialized with either a manifest URL or an already parsed manifest. Additionally, there are several objects that the player provides for loading and parsing manifests that will be useful in this process. This change provides for the use of these objects outside the player along with simplifying the player's internal handling of manifests and manifest updates.

Please see commit comments in 954ece0 for more details.