Add optional WIDTH and HEIGHT arguments to GUI_FILLER

data/gui/macros/filler.cfg

@@ -1,11 +1,23 @@
 #textdomain wesnoth-lib
+
 # Defines the default spacer used to fill a grid cell.
 # This is needed since empty cells aren't allowed.
 
 #define GUI_FILLER
+
+#arg WIDTH
+0 #endarg
+
+#arg HEIGHT
+0 #endarg
+
 	[column]
+		grow_factor = 0
+
 		[spacer]
+			width = {WIDTH}
+			height = {HEIGHT}
 		[/spacer]
+
 	[/column]
 #enddef
-