Improve build and widget storage

There are no longer any qt headers included in wx/qt headers.
Applications do not need to link with qt librarys anymore, only wxqt libraries.
wxWindow and derived widgets only contain one pointer to their qtwidget, no longer
  carrying both base and derived pointers in parallel as was before.

include/wx/qt/glcanvas.h

@@ -8,7 +8,11 @@
 #ifndef _WX_GLCANVAS_H_
 #define _WX_GLCANVAS_H_
 
-#include <QtOpenGL/QGLWidget>
+#include <GL/gl.h>
+
+class QGLWidget;
+class QGLContext;
+class QGLFormat;
 
 class WXDLLIMPEXP_GL wxGLContext : public wxGLContextBase
 {
@@ -54,8 +58,6 @@ public:
 
     static bool ConvertWXAttrsToQtGL(const int *wxattrs, QGLFormat &format);
 
-    virtual QGLWidget *GetHandle() const { return static_cast<QGLWidget *>(m_qtWindow); }
-
 private:
 
 //    wxDECLARE_EVENT_TABLE();