This makes it more flexible to match resources that may have complex
properties. A typical case in which you would need this is if you have
resources that have JSON embedded in a string on which you might want
to do structural matching.

Supports both Alarms and Dashboards. Adds a 'Metric' abstraction
which can be exposed by other resources.

- Metric providers on resources are now functions.
- Add integration test.
- Add unit tests on graphs.
- Introduce tokenAwareJsonify() which was necessary to properly create a dashboard
  with references to alarms in it.