Explicitly state type of source

To avoid errors when constructing IdentifierScope
Add a FindExpressionAtRange function

Which uses the already implemented TryFindExpressionAtRange
Make ExtractFunction use IdentifierScope

Also added an ExpressionScope which can be used for ScopeTrees which
don't just declare identifiers.
Use IdentifierScope.FindReferences in AddArgument
Project test fixture with SetUp and TearDown methods
Add a class containing info about the project
Replace source by project in all the refactorings
Remove the monodevelop add-in

It is part of fsharpbinding's MonoDevelop add-in