Rename Controls component variable accessing engine

lib/components/controls_component.dart

@@ -15,27 +15,27 @@ import 'package:rules_of_living/service/engine_service.dart';
   styleUrls: const ["controls_component.css"],
 )
 class ControlsComponent {
-  final EngineService ctrl;
+  final EngineService engine;
 
-  ControlsComponent(this.ctrl);
+  ControlsComponent(this.engine);
 
   void onStartClicked() {
-    ctrl.toggleRunning();
+    engine.toggleRunning();
   }
 
   void onStepClicked() {
-    ctrl.step();
+    engine.step();
   }
 
   void onResetClicked() {
-    ctrl.reset();
+    engine.reset();
   }
 
   void onRandomClicked() {
-    ctrl.addRandomPattern();
+    engine.addRandomPattern();
   }
 
   void onClearClicked() {
-    ctrl.clear();
+    engine.clear();
   }
 }

lib/components/controls_component.html

@@ -1,7 +1,7 @@
 <div id="controls">
     <material-button id="reset" (click)="onResetClicked()"><material-icon icon="replay" baseline></material-icon></material-button>
     <material-button id="run" (click)="onStartClicked()">
-        <span [ngSwitch]="ctrl.isRunning">
+        <span [ngSwitch]="engine.isRunning">
             <material-icon *ngSwitchCase="false" icon="play_arrow" baseline></material-icon>
             <material-icon *ngSwitchCase="true" icon="pause" baseline></material-icon>
         </span>