Added backend services resource to gce compute
Added backend services example and model classes
Merge pull request #3069 from snyquist2/gce_l7

[google|compute] Add backend services resource for L7 load balancing
Whitespace cleanup of #3069.
[google|monitoring] Add support for Google Cloud Monitoring

- Add models, requests, tests & examples for Timeseries
- Add models, requests, tests & examples for TimeseriesDescriptors
- Add models, requests, tests & examples for MetricDescriptors