Implement Engine Step Method

lib/app_component.dart

@@ -39,8 +39,7 @@ class AppComponent implements OnInit {
   }
 
   void onStepClicked() {
-    engine.running = false;
-    engine.update();
+    engine.step();
   }
 
   void onResetClicked() {

lib/src/Engine.dart

@@ -60,6 +60,10 @@ class Engine {
   void update() {
 //    print("updating");
     if(!grid.update()) running = false;
+
+  void step() {
+    running = false;
+    _grid.update();
   }
 
   void render([num interp]) {