Added: Skip ad button (WIP)
NOTE: There is some placeholder logic in here (i.e. triggers EndPreroll when skipped [firing 'complete' beacons]
Changed: Skip ad button to be function driven instead of event driven.
Added: Configurable duration for skip ad button (reads from preroll)
Changed: Cleaned up some skip ad button code.
Added: Skip ad button animations and styling hooks.
Removed: Fade effect of skip ad button. (Because of dependency on jQuery.)
Cleaned up some skip ad code. (Moved actual skipping logic outside the button to the VJS player level.)