Windows Qt 5 build fixes

The issue is that there's a distinction between UNICODE and _UNICODE
on Windows, to prevent build errors like TCHAR being a wchar but _tcsrchr
expects a char*

Additionally I get some issues under Qt5 by including <QtGui> it loads
the qt gl function loader and fucks with GLEW. I'd love to see a better
solution without an ifdef, so discuss before merging.