Add AS::Notifications to YouTube requests

Opening this PR for discussion.

ActiveSupport::Notifications, by convention, should be namespaced right-to-left, so I've named this `request.yt` (feel free to change this though).

Could be useful for:
  * Quota / Request analysis
  * Time spent making YouTube requests
  * Audit Trails
Ahh that's great. I like that!  Passing in the response could actually be very useful as well.