Initial version of FSharp unit test text editor extension

This is not quite yet ready for merge as there are a number of issues:

* Running or debugging a single instance of a test doesn't appear to do anything.
* Symbols appear as expected in margin, `Run all` and `Debug all` seem to work ok.

- - -
I suspect the issues are to do with naming semantics of nrefactory.  
We are currently using `TypeName` + `.` + `MethodName`, I also suspect double tick methods are not been treated correctly.