PCB common library header rationalization.

* All header files used to create the PCB common library now compile as
  stand alone code.  This prevents the need to define them in a specific
  order to make source code compile properly.  It should also now be
  possible to relocate the source code to build the common PCB library
  to a separate folder.

common/class_layer_box_selector.cpp

@@ -3,12 +3,13 @@
 #include "wxPcbStruct.h"
 #include "class_board_design_settings.h"
 #include "colors_selection.h"
-
+#include "layers_id_colors_and_visibility.h"
 #include "bitmaps.h"
-
 #include "hotkeys.h"
 #include "help_common_strings.h"
 
+#include "class_board.h"
+
 #include <wx/ownerdrw.h>
 #include <wx/menuitem.h>
 #include <wx/bmpcbox.h>