Move uncommon workboard management options to "Manage Board" view

Summary:
This gives us room for less-common workboard management options like "Disable Board" without overloading the menus on the main board.

Particularly, we can add background color options here without anything getting weird.

I've left "Add Column" on the main UI since I think it's common enough to leave there. We could probably move "Hide Column" to this UI in the future, though.

Test Plan:

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D15278