R1:bc591b1b5f7d

Mostly move workboard card moves to new Workboard code

Summary:
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.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4900

Differential Revision: https://secure.phabricator.