Add Google calendar publish agent

* Adds VCR (it was tricky to mock the oauth)
* Adds Google calendar publish agent
* Adds a helper library to make fetching events easy


![screenshot from 2014-06-29 03 10 04](https://cloud.githubusercontent.com/assets/365751/3421405/4ed472c2-feeb-11e3-900c-2c42c2a5c70d.png)

![screenshot from 2014-06-29 03 10 14](https://cloud.githubusercontent.com/assets/365751/3421406/4ed8636e-feeb-11e3-8508-583675a68f27.png)

Its a real one, for a real service account, but it's a service account I've deliberately set up for testing this functionality.
If other maintainers need to make a new service account and regenerate the tests because this one is dead, the markdown in the class should be enough,