Swap "Create Task" button over to EditEngine

Summary: Ref T9132. I can't actually get rid of the EditController yet since a few weird things still use it, but I think I can swap this button out without breaking anything. This will let us do "New Feature Request" / "New Bug" / "Advanced Task Creation" on secure and start playing with this stuff sooner.

Test Plan: Clicked "Create Task", got sent to new form.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9132

Differential Revision: https://secure.phabricator.com/D14673