Give the workboard "default" workflows more modern state handling

Summary:
Depends on D20628. Ref T4900. Currently, the "Save Current Order/Filter As Default" flows on workboards duplicate some state construction, and require parameters to be passed to them explicitly.

Now that state management is separate, they can reuse a bit more code and be made to look more like other similar controllers.

Test Plan:

• Changed the default order of a workboard.
• Changed the default filter of a workboard.
• Changed the order of a board to something non-default, then changed the filter, then saved the new filter as the default. Saw the modified order preserved and the modified filter removed, so I ended up in the right ("most correct") place: on the board, with my custom order in a URI parameter, and no filter URI parameter so I could see my new default filter behavior. This is an edge case that's not terribly important to get right, but we do get it right.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T4900

Differential Revision: https://secure.phabricator.com/D20629