R1:82e67e6bb971

Clean up some EditEngine meta-policies

Summary:
Ref T9908. Simplify some of the policies here:

- If you can edit an application (currently, always "Administrators"), you can view and edit all of its forms.
- You must be able to edit an application to create new forms.
- Improve some error messages.
- Get about halfway through letting users reorder forms in the "Create" menu if they want to sort by something weird since it'll need schema changes and I can do them all in one go here.

Test Plan…