Handle snapshots directly before and after ad playback

Instead of taking the player snapshot some of the transitions before entering ad-playback and restoring the snapshot in another set, tie the management of the player snapshot directly to the ad-playback state. This issue arose when contentupdate was fired for a video that had already played a preroll and and the ad response for the next video timed out. Since the snapshot was restored moving into ads-timeout-playback and no new snapshot had been taken at contentupdate, the original video was restored. Now, moving to ads-timeout-playback does not restore a player snapshot and snapshot handling is much more localized to the ad-playback state.