Adding in API to allow for DVR information used to drive a player UI

Added new class called videoElementExt with and API to help with DVR window. We could add other video element API to this as well in the future. Added metric to hold the information for DVR streams. Wanted the API to be a singleton and the metric VO to just hold the values for the API to use.
Yes, I understand. If the goal is a unified interface, then the MediaPlayer object is supposed to be that interface.

I do feel concerned about a unified interface though if the time values are shifting relative to a moving window in DVR mode but fixed for VOD.