Changed Testframework to NUnit

In the first step I ran all tests on my machine. All tests not running successfully were ignored. In the second step I switched the testing framework to nunit in version 2.6.3.

In order to be able to run the tests within VS 2012 / 2013 you have to install the Nunit Test Adapter available in Visual Studio Gallery
http://visualstudiogallery.msdn.microsoft.com/6ab922d0-21c0-4f06-ab5f-4ecd1fe7175d

Issue #7