[google|monitoring] Add support for Google Cloud Monitoring

This commit adds the initial support for [Google Cloud Monitoring](https://developers.google.com/cloud-monitoring/)

- Add models, requests, tests & examples for Timeseries
- Add models, requests, tests & examples for TimeseriesDescriptors
- Add models, requests, tests & examples for MetricDescriptors
Could you call this a timeseries and timeseries a timeseriescollection?