add property groups

Currently, the only way to define standard properties for a bunch of devices is to assign those to a group, then assign devices to that group (we do this most often with location, but it applies as well to other common settings like SNMP parameters, pointers to support information, etc.).  This works for devices, but leads to numerous problems (e.g., it breaks RBAC), and those do not apply to other objects like Services (I refuse to start calling those Websites as a ping check to a firewall is not a Website).  A solution for this would be to allow creation of property groups that can then be bound to any object.  The main goal is to avoid repeatedly defining the same thing across many objects so changes later can be made efficiently and without error.

Thanks,
Mark