Prepare Engine for Button responses

lib/src/App.dart

@@ -27,6 +27,11 @@ class App {
     _elapsed.start();
   }
 
+  void reset () {
+    grid = new Grid(100, 100);
+    running = false;
+  }
+
   void process(num now) {
     _drawLag+= _elapsed.elapsedMilliseconds;
     _updateLag += _elapsed.elapsedMilliseconds;
@@ -38,7 +43,7 @@ class App {
         print("ERROR STUCK IN UPDATE LOOP");
         break;
       }
-      update();
+      if (running == true) update();
       _updateLag -= _MS_PER_STEP;
     }
 
@@ -50,7 +55,7 @@ class App {
 
   void update() {
 //    print("updating");
-    if (running == true) grid.update();
+    grid.update();
   }