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.

pcbnew/edit_track_width.cpp

@@ -4,12 +4,15 @@
  */
 
 #include "fctsys.h"
+#include "gr_basic.h"
 #include "class_drawpanel.h"
 #include "confirm.h"
+#include "wxPcbStruct.h"
+
+#include "class_board.h"
+#include "class_track.h"
 
 #include "pcbnew.h"
-#include "wxPcbStruct.h"
-#include "class_board_design_settings.h"
 #include "drc_stuff.h"
 #include "protos.h"