membership dashboard improvements

attached patches extend the membership dashboard so that calculations are generated for just the primary members as well as all. this is most useful for orgs that make use of membership inheritance via relationships, as the current dashboard has limited utility in such situations (orgs typically would count the number of members based on who "owns" the membership – not the number of related members).

this also allows forcing a search to retrieve just primary members via GET url variable (similar to what we do with other options)