Fixup Windows platform for UTF8.
* Added Widen and Narrow functions. UTF8 <-> UTF16 conversion. C++11.
* Fix OpenGL samples.
Move Widen and Narrow to Utility.
* Move to Gwen::Utility so can be more widely used.
Fix wide strings in UnitTests
* Need to convert wide strings to narrow otherwise format is wrong.
Fix DirectX9 for wide to narrow conversion
Fix GDI+ sample for narrow/wide conversion.