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.

src/qt/bitmap.cpp

@@ -24,6 +24,7 @@
 #include "wx/bitmap.h"
 #include "wx/cursor.h"
 #include "wx/rawbmp.h"
+#include "wx/qt/colour.h"
 #include "wx/qt/private/converter.h"
 #include "wx/qt/private/utils.h"
 
@@ -213,8 +214,6 @@ wxBitmap::wxBitmap(const wxImage& image, int depth, double WXUNUSED(scale) )
 wxBitmap::wxBitmap(const wxCursor& cursor)
 {
     // note that pixmap could be invalid if is not a pixmap cursor
-    // also, a wxCursor::GetHandle method could be implemented instead of 
-    // accessing the member variable directly  
     QPixmap pix = cursor.GetHandle().pixmap();
     m_refData = new wxBitmapRefData(pix);
 }