Remove unnecessary pattern parameters

lib/src/Engine.dart

@@ -124,20 +124,8 @@ class Engine {
     if (canvas != null) _grid.render(canvas, interp);
   }
 
-  void addPattern(
-      {CellPattern pattern,
-      int x,
-      int y,
-      int amount,
-      int dispersal,
-      int seed}) {
-    _grid.addPattern(
-        pattern: pattern,
-        x: x,
-        y: y,
-        amount: amount,
-        dispersal: dispersal,
-        seed: seed);
+  void addPattern({int amount, int dispersal}) {
+    _grid.addPattern(amount: amount, dispersal: dispersal);
   }
 
   void toggleEdgeRendering() {