Post tests

First pass at adding some tests for Post models and collection.

* Test default values
* Test setting values
* Test parse (on sync)
* Test getting parent method.

I have added Sinon.js to handle mock server responses. It can do other stuff useful for testing - although i'm not using it. 

Also - Sinon is added as a bower package using a URL. This is because the package on bower doesn't contain compiled files and not reccommended for use. There is a 3rd party compiled package available but I thought it more reliable to do it this way.