Only offer Visibility options for UIExtensionClass when permissions allow it

Right now we regularly have problems when users add UIExtensionClass xobjects because they don't know the requirements about the scope:

• You need to have admin permissions for the "Current Wiki" scope
• You need to have programming rights for the "Global" scope

This is for example the case with the Menu application which, under the good, uses an UIExtensionClass xobject.

So the idea is to offer only the scope options that are allowed for the current user.