Simplify UI for browsing

From Gary Brown:

These are the signatures that would help simplify the UI for browsing:

GrouperStem:
public Set getChildGroups(AccessPrivilege[] privileges)
public Set getChildStems(NamingPrivilege[] namingPrivs, AccessPrivilege[] accessPrivs)
public Set getChildStems(NamingPrivilege[] namingPrivs)
public Set getChildStems(AccessPrivilege[] accessPrivs)

Child groups are straightforward. Child stems are an `OR` on the GrouperSession subject having one of the AccessPrivileges on any descendant Group, or NamingPrivilege on any descendant Stem

Group /stem searching would benefit from similar methods, though stem searching would generally return stems where the GrouperSession subject had CREATE or STEM privilege.

Not sure if this would be best done as filters or an additional argument to the createQuery method or getGroups.getStems

When listing memberships the UI shows the number of paths by which a subject is a group member. In order to do this I use a getMemberships call and iterate through the whole membership coming up with a list - of `unique` subjecta and the count for their occurrence. As I`m using Maps to wrap objects in the UI I set the occurrence count on the Map. It would
simplify the UI if the API were able to do something similar - a getMembersWithCount. I`m not sure there is a particularly clean way to do this - but there are several kludgy ones e.g. return a Set implementation that can be cast to something with a getCount(Subject subj) method.