WX: HiDPI: MemcardManager

Required a partial rewrite of the image loading code because it was working in
unscaled wxBitmaps. Needed to make it produce wxImages and scale them instead.

Source/Core/DolphinWX/MemcardManager.h

@@ -131,5 +131,6 @@ private:
     void OnRightClick(wxMouseEvent& event);
   };
 
+  wxSize m_image_list_size;
   CMemcardListCtrl* m_MemcardList[2];
 };