Add destroy method to Keymaps

src/editor/model/Editor.js

@@ -772,7 +772,7 @@ export default Backbone.Model.extend({
     UndoManager.clear().removeAll();
     Panels.getPanels().reset();
     Canvas.destroy();
-    Keymaps.removeAll();
+    Keymaps.destroy();
     RichTextEditor.destroy();
     LayerManager.destroy();
     AssetManager.destroy();

src/keymaps/index.js

@@ -213,6 +213,11 @@ export default () => {
     removeAll() {
       Object.keys(keymaps).forEach(keymap => this.remove(keymap));
       return this;
+    },
+
+    destroy() {
+      this.removeAll();
+      [em, config, keymaps].forEach(i => (i = {}));
     }
   };
 };