Fix deprecated jQuery method in toolbar

src/js/theme/toolbar.js

@@ -13,7 +13,7 @@ function generateId() {
 
 // Insert a jquery element at a specific position
 function insertAt(parent, selector, index, element) {
-    var lastIndex = parent.children(selector).size();
+    var lastIndex = parent.children(selector).length;
     if (index < 0) {
         index = Math.max(0, lastIndex + 1 + index);
     }