Allow menu items to be edited again

Summary:
Ref T12174. We now require that we can figure out a valid "edit mode" (global vs custom/personal) before we hit EditEngine. Since the EditEngine routes don't have an itemID, they would failu to figure out the mode and just 404.

Let the engine use id (from EditEngine) if itemID (from MenuEngine) isn't present in the route.

Test Plan:

• Edited some menu items on Home / Projects.
• (I think I tested this, then broke it, originally.)

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12174

Differential Revision: https://secure.phabricator.com/D17280