On workboards, provide all of the supported "create task" forms in the dropdown

Summary:
Ref T12314. Ref T6064. Ref T11580. If an install defines several different task create forms (like "Create Plant" and "Create Animal"), allow any of them to be created directly onto a workboard column.

This is just a general consistency improvement that makes Custom Forms and Workboards work together a bit better. We might do something fancier eventually for T6064 (which wants fewer clicks) and/or T11580 (which wants per-workboard control over forms or defaults).

Test Plan:

• Created several different types of tasks directly onto a workboard.
• Faked just one create form, saw the UI unchanged (except that it respects any renaming).

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12314, T11580, T6064

Differential Revision: https://secure.phabricator.com/D17446