Initial configuration of the GHUnit testing framework

This includes the initial configuration of the GHUnit testing framework I mentioned in #23 so that asynchronous test cases are supported. I added a separate target in the project.

The tests run in the simulator and on an armv7 device but armv7s (iPhone 5) is not yet supported. The only device I tested is the iPad 3.

I've also added the login test that I was working on before. It is updated for the latest code.