Clean up "reorder" permissions in MenuEngine for personal favorites
Most other edit operations only test for edit capability on the MenuItem itself, which we already do correctly. However, because reordering affects all items, we test for capability on the object.
Weaken this when reordering custom items.
Test Plan: Reordered custom items in Favorites as a non-administrator.
Reviewed By: chad
Maniphest Tasks: T12159
Differential Revision: https://secure.phabricator.com/D17257