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() {

lib/src/Simulation.dart

@@ -13,7 +13,6 @@ class Simulation {
   bool _dirty = true;
   bool _renderEdges = true;
 
-  int _startingSeed;
   int _amount;
   int _dispersal;
 
@@ -30,19 +29,13 @@ class Simulation {
     _dirty = true;
   }
 
-  void addPattern(
-      {CellPattern pattern,
-      int x,
-      int y,
-      int amount,
-      int dispersal,
-      int seed}) {
-    _startingSeed = seed ?? DateTime.now().millisecondsSinceEpoch;
+  void addPattern({int amount, int dispersal}) {
+    int _startingSeed = DateTime.now().millisecondsSinceEpoch;
     math.Random rng = new math.Random(_startingSeed);
     _amount = amount ?? rng.nextInt(20);
     _dispersal = dispersal ?? 10;
-    int cx = x ?? rng.nextInt(map.width ~/ 3) + (map.width ~/ 3);
-    int cy = y ?? rng.nextInt(map.height ~/ 3) + (map.height ~/ 3);
+    int cx = rng.nextInt(map.width ~/ 3) + (map.width ~/ 3);
+    int cy = rng.nextInt(map.height ~/ 3) + (map.height ~/ 3);
 
     int sanityCheck = 0;
     for (var i = 0; i < (_amount); i++) {