Extract EngineService into separate service

lib/service/engine_service.dart

@@ -1,48 +1,15 @@
-import 'dart:html' as html;
-
 import 'package:rules_of_living/src/Engine.dart';
 
 class EngineService {
-  Engine _engine;
+  Engine _uncachedEngineAccess;
 
-  Engine get engine => _engine ?? getEngine(Engine());
-
-  Engine getEngine(Engine engine) {
-    _engine = engine;
-    return _engine;
+  Engine get engine => _uncachedEngineAccess ?? _setCachedAndReturn(Engine());
+  void set engine(Engine newEngine) {
+    _uncachedEngineAccess = newEngine;
   }
 
-  void set canvas(html.CanvasElement canvas) => engine.canvas = canvas;
-  html.CanvasElement get canvas => engine.canvas;
-
-  void run() {
-    engine.running = true;
+  Engine _setCachedAndReturn(Engine newEngine) {
+    engine = newEngine;
+    return newEngine;
   }
-
-  void stop() {
-    engine.running = false;
-  }
-
-  void toggleRunning() {
-    engine.running = !engine.running;
-  }
-
-  void step() {
-    engine.step();
-  }
-
-  void reset() {
-    engine.reset();
-  }
-
-  void addRandomPattern() {
-    engine.running = false;
-    engine.addPattern();
-  }
-
-  void clear() {
-    engine.clear();
-  }
-
-  bool get isRunning => engine.running;
 }