Clean up MonoDevelop.UnitTesting

[tstivers1990]

I've cleaned up some of the code to make it more readable.

I also made UnitTestGroup abstract, as it is never directly instantiated, and is always derived from. I feel this is better for clarity. Specifically, it removed the need for one of the methods to be blank, rather than abstract like it should be.

I also removed commented code, excess whitespace, redundant casts, redundant namespace specifications and any methods or fields I came across that weren't being used.