R1:b2de1490093c

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…