Clean up some EditEngine meta-policies
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.
- Tried to create and edit forms as an unprivileged user.
- Created and edited forms as an administrator.
Reviewed By: chad
Maniphest Tasks: T9908
Differential Revision: https://secure.phabricator.com/D14700