[UX] Allow image styles to be ordered/sorted.

I'm not sure if there is an order to image styles already, but I'd really like the ability to order mine in the select list used to choose one. I think this could be accomplished by adding tabledrag to the image styles list, storing the order, then sorting the styles in the select list by this order.

Tasks remaining - find out if there is a weight or key we can use for sort order (if not, add one) - add tabledrag to the image styles UI to set the order - update the query that retrieves image styles to sort by this order