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.
Thank you Kirk for the quick feedback.   I thought this would be brought up.  Here is why I chose that name.  We do not want to use names like DVRWindow or DVRWindowExtensions  because as a player developer with a custom control bar,  it is preferable to get your time/duration and seek commands from the same API calls for VOD and live streams with DVR.  I would not like to have to get one set of information from the video element and another from this class just because we do the offsets and calculations.      This is why I chose VideoElementExt.   I do agree that this Ext naming is reserved for what you mentioned.  That being said,  i think there may be some things in the class now that could be extended depending on the functionality you want.  For example, you may want to override duration or time to return live if you are within X amounts of seconds to live-edge etc.   I can change the name to something else if you really think it is best but wanted to respond with this before I make any changes.