Introduce pagination panel (fixes #141)

Change-Id: Ib8522c4d154b96630abcd23c7115b2fb4633bdfb
diff --git a/dev/js/src/buttongroup.js b/dev/js/src/buttongroup.js
index 85c6555..31f60c8 100644
--- a/dev/js/src/buttongroup.js
+++ b/dev/js/src/buttongroup.js
@@ -129,12 +129,13 @@
         this._omOutside ? true : false,
       );
       
-      this.add(title, data, function (e) {
+      let b = this.add(title, data, function (e) {
         list.show();
         list.button(this.button);
         list.focus();
       });
-      return list;
+      b.list = list;
+      return b;
     },
 
     /**