add moveToTop and moveToBottom buttons

[schwer]

For larger list of selected items, it's useful to be able to move the selected items to the top or bottom of the list in one click, rather than clicking multiple times. I've penciled in red in the mockup above what I have in mind.

[jakezatecky]

Good suggestion. It is a natural extension of the "move all left" and "move all right" buttons, but for ordering.