Learning to love py.test

I've been aware of py.test for a long time but it's only tonight that I've fallen in love. 

This PR adds support for using py.test within the boilerplate project. It also provides example unit, integration and functional tests that illustrate the power and simplicity of py.test. For instance, there are 3 functional tests that do the same simple test but using:

- The Django test client (6a0343d)
- Webtest (2ecb520)
- Selenium Webdriver (66746b3)

Hopefully this will be the start of a long and fruitful relationship.