Re-enable by cell grouping

I think that in the long run it's more reliable to do it outside of
graphite.

Change-Id: Id0950af11d2cbdd51bf97bff71e33162f38e7349
Fix bug in by_domain

Instead of processing the known users, it exits if a user can't be
found.

Change-Id: I9167969603cdb1ac3182dafb7f925dbcf4c9fa5d
Initial implementation of user count

Change-Id: I1f41eff1b02d0e98436b982422d00e56c45ceba1