Fix GtkTestRunner so that test assembly is added to NUnit args

So far, tests haven't been run!
[Drawing API] Add ModifyCTM (Matrix m) to Xwt.Drawing.Context API

This provides the link between the Matrix transforms facilities and Drawing.Contexts
An sample of using this for specialised transforms has been added to DrawingTransforms.cs
and unit tests hve been aded to Testing/Tests/TransformTests.cs
Merge pull request #232 from hwthomas/master

[Drawing API] Add ModifyCTM to DrawingContext