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.

Partly because of the complexity of having to filter up the exceptions through the model and controller in order to capture the error state strings in the flash messages.  Partly because of my indecision about where the abstraction lies between user input conventions and what is to be known to the model.