VS: Resx-file support update.

This is the first time I try to make a pull request, so if I'm doing something wrong please help me correct it.

In my project group we are using CMake to generate c++/cli winform projects and I noticed the work done in "VS: Add Windows Forms Support" was in the right direction for solving some of the problems we were facing.

The changes as submitted was breaking some functionality in our projects, so I made some changes that fixes our problems and I believe that it will also work for others.
Existing VSWindowsFormsResx Test project is also working with my changes.

Please see detailed comments in specific commits.