Move workboard "filter" workflow to a separate controller

Summary:
Depends on D20629. Ref T4900. Currently, the "Advanced Filter..." workflow on workboards (where you build a custom query) is inline in the main board controller.

This is because the filter flow depends on some of the board view state: we want to start with the current filter applied to the board, and preserve other state after you change the filter.

Now that ViewState can handle state management, we can separate this stuff out pretty easily.

Test Plan:

• Changed filters on a board.
• Applied a custom filter to a board.
• Changed the ordering of a board, then applied a custom filter. Verified "Cancel" and "Apply Filter" both preserve the order state.
• Changed the ordering of a board, then applied a custom filter, intentionally making a mistake in configuring the filter by entering an invalid date. Saw a dialog with an error. After correcting the error, saw state preserved properly.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T4900

Differential Revision: https://secure.phabricator.com/D20632