expose layer

Author: i-make-robots

src/main/java/com/marginallyclever/makelangelo/donatelloimpl/nodes/turtle/PrintTurtle.java

@@ -41,6 +41,7 @@ public PrintTurtle() {
         addPort(showTravel);
         addPort(travelColor);
         addPort(lineThickness);
+        addPort(layer);
     }
 
     @Override