Custom tag for buttons in Panels module. Closes #1787

src/panels/model/Button.js

@@ -4,6 +4,7 @@ module.exports = Backbone.Model.extend({
   defaults: {
     id: '',
     label: '',
+    tagName: 'span',
     className: '',
     command: '',
     context: '',

src/panels/view/ButtonView.js

@@ -3,7 +3,9 @@ import { isString, isObject, isFunction } from 'underscore';
 const $ = Backbone.$;
 
 module.exports = Backbone.View.extend({
-  tagName: 'span',
+  tagName() {
+    return this.model.get('tagName');
+  },
 
   events: {
     click: 'clicked'