OG listing improvements

[holtzermann17]

Be able to list groups (http://metameso.org/q/groups) in some more useful ways, e.g. by "recently active", "my groups", "include co-author groups", sort them using MSC categories, etc., and be able to search them (compare the user list, which can be searched/filtered by forename, surname, or username).

Note that there will be various "listings" that we will want to be able to handle in roughly the same way; this can serve as a prototype.