Make panels more configureable through attributes

src/panels/model/Panel.js

@@ -8,6 +8,7 @@ module.exports = Backbone.Model.extend({
     content: '',
     visible: true,
     buttons: [],
+    attributes: {}
   },
 
   initialize(options) {

src/panels/view/PanelView.js

@@ -29,6 +29,10 @@ module.exports = Backbone.View.extend({
     this.$el.html(this.model.get('content'));
   },
 
+  attributes() {
+    return this.model.get('attributes');
+  },
+
   initResize() {
     const em = this.config.em;
     const editor = em ? em.get('Editor') : '';