improve *Group TicketSQL (WatcherGroup, CCGroup, ...)

* add OwnerGroup
* support name in addition to id, name means user defined group
* make it clear that only '=' op is supported
* simplify code by using existing API
* add tests
show *Group TicketSQL in the query builder
Remove out of date and misleading POD
Merge branch '4.2/xxxgroup-ticketsql'

Conflicts:
	lib/RT/Tickets.pm