Implemented MonitoringSupport.

Available actions are:
* List alarms (with filter options)
* List metrics (with filter options)
* Add/update alarm
* Remove alarms
* Enable alarm actions
* Disable alarm actions

Mainly all new code except but also changed CloudWatch API version to 2010-08-01.

Corresponding core changes: https://github.com/greese/dasein-cloud-core/pull/52