Hide Implementation of edge rendering in grid

lib/app_component.dart

@@ -54,7 +54,7 @@ class AppComponent implements OnInit {
   }
 
   void onEdgesClicked() {
-    engine.grid.switchEdgeRendering();
+    engine.toggleEdgeRendering();
   }
 
   void onClearClicked() {

lib/src/Engine.dart

@@ -65,6 +65,8 @@ class Engine {
   void render([num interp]) {
 //    print("rendering");
     grid.render(canvas, interp);
+  void toggleEdgeRendering() {
+    _grid.renderEdges = !_grid.renderEdges;
   }
 
   void set running(bool on) => _running = on;

lib/src/Grid.dart

@@ -210,6 +210,9 @@ class Grid {
 
   void switchEdgeRendering([bool on]) {
     _renderEdges = on ?? !_renderEdges;
+  void set renderEdges(bool on) {
+    _renderEdges = on;
     _dirty = true;
   }
+  bool get renderEdges => _renderEdges;
 }