Implement wxDC coordinate handling and wxGCDC.

* Implement code to allow wxDC to handle coordinate conversions between
  device and drawing units.
* Add build settings to enable wxGCDC for wxGraphicsContext testing.
* Remove wxAUI conditional build cruft as it is now required to build
  Kicad.
* Fix scroll increment size regression to prevent jumping around the
  zoom center position.
* Add find GDI+ cmake module for building on WXMSW when wxGraphicsContext
  is enabled.

common/block_commande.cpp

@@ -101,6 +101,7 @@ void BLOCK_SELECTOR::Draw( WinEDA_DrawPanel* aPanel, wxDC* aDC,
                            int aDrawMode,
                            int aColor )
 {
+
     int w = aPanel->GetScreen()->Scale( GetWidth() );
     int h = aPanel->GetScreen()->Scale( GetHeight() );