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.
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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.