Reorder videos

This implements functionality to allow user to reorder videos in their queue and to change ratings on the fly.
Note that because of extensive error checking, I could not make the controller code as skinny as I would have liked.  There remains a fair amount of logic still in the controllers.

Also, would like to get feedback on whether the Video class is the right place to put some logic related to updating review ratings for the videos.

I'd suggest that if the validation is more data oriented, keep them in the models; if they are more "rules" oriented (make sure the user is at least 18 yo to buy a beer) or relating to multiple models then keep them in the controller (and in this case you porbably don't want to call them validations; validations in Rails carries a specific meaning)