Multiple Google Cloud Platform improvements and new resources

Added: HttpHealthCheck, ForwardingRule, TargetPool  (together they provide network / layer3 load balancing)
Modified Instance: added service account + scopes
Modified Address: added selfUrl

There is currently no documentation, I'd like to get some eyeballs on this first.
That would make us incompatible with the naming in the APIs, but as long as it's consistent I guess it's OK.  The APIs have anomalies anyway (IPAddress should be ipAddress).