Making rsGroupInfoManager non-static in RSGroupAdminEndpoint
Encapsulate RSGroupAdminService into an internal class in RSGroupAdminEndpoint (on need of inheritence).
Make RSGroupAdminEndpoint extend BaseMasterObserver, so got rid of unwanted empty implementations.
Change two internal classes in RSGroupAdminServer to non-static (so outer classes' variables can be shared).
Rename RSGroupSerDe to RSGroupProtobufUtil('ProtobufUtil' is what we use in other places). Moved 2 functions to RSGroupManagerImpl because they are only used there.
Major 