Add a "make the workboard the default view" checkbox when creating a workboard

Summary: Ref T10054. Since we no longer have the "workboard default if it exists" rule, provide a quick way to make it the default.

Test Plan: Created a new workboard with the box checked, saw menu change appropriately.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10054

Differential Revision: https://secure.phabricator.com/D15092