Mostly move workboard card moves to new Workboard code
Ref T4900. This gets moves on the new stuff and cleans them up a little.
Two behaviors haven't been ported yet: height adjustment during drags (which is broken anyway with inner scroll) and updating point counts (coming soon).
Test Plan: Dragged cards around on a board, including top/bottom positions and normal/priority sort.
Reviewed By: chad
Maniphest Tasks: T4900
Differential Revision: https://secure.phabricator.com/D15226