PCBNEW: Re-add missing SWIG zone filler

Zone filler was factored out into a separate header.  To allow python
access to zone filling, we need to include the revised signatures.

pcbnew/swig/zone.i

@@ -2,8 +2,10 @@
 
 %include class_zone.h
 %include zones.h
+%include zone_filler.h
 %{
 #include <class_zone.h>
 #include <zones.h>
+#include <zone_filler.h>
 %}