video js: add methods for controlling the video loop property
video js: add methods for controlling the video loop property

I add a `getLoop` method to abstract the property lookup logic since
the native video object doesn't know anything about loop settings.
The other methods are similar to the mute setting methods.  Note:
I manually publish loop setting events as the native video object
doesn't do it for me like it does for the mute settings.

redding/romo-av,redding/romo-av