In MAGNOLIA-6615, we agreed to differentiate and introduce #getAllSuperGroups and #getAllSubGroups. We only did so on MgnlGroupManager concrete impl, for binary compatibility reasons.

With 5.5, we introduce this into the GroupManager interface straight. We move the javadoc up a level, and then deprecate GroupManager#getAllGroup, which was ambiguous.

We might as well address other few points from the related concept (sections 1b, 2, 3 and 6) if there's any easy target, or keep that as other follow-ups.