Clean up modules listing

I'm trying to get the modules listing in admin/build/modules a little bit cleaned up.

Right now 'DB Maintenance' is listed as the only item in a separate group "Administration utility" (in db_maintenance.info: package = "Administration utility").

As this adds to the shattered listing we have at the moment, I propose moving the module to the already populated group "Administration" (package = Administration.)

If there is some support for it or at least no objection, I will provide a patch within the next days.