We have to deprecate all classes in this module so to encourage users (and ourselves, of course) to port existing modules to 5.0. Need to decide how to word the deprecation msg (I imagine it has to be something more elaborate than just "deprecated since 5.0"). I guess we also should set from the very beginning the magnolia_ui version (5.1?) which will see the removal of this compatibility module and state it in the deprecation text.