Add addPattern Functionality to Engine

lib/app_component.dart

@@ -49,6 +49,7 @@ class AppComponent implements OnInit {
 
   void onRandomClicked() {
     engine.running = false;
+    engine.addPattern();
   }
 
   void onEdgesClicked() {

lib/src/Engine.dart

@@ -72,6 +72,17 @@ class Engine {
     _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 toggleEdgeRendering() {
     _grid.renderEdges = !_grid.renderEdges;
   }