Enable add a cell button

Author: tuncbkose

packages/notebook-extension/style/base.css

@@ -124,8 +124,6 @@ body[data-notebook='notebooks']
 
 /* Tweak the notebook footer (to add a new cell) */
 body[data-notebook='notebooks'] .jp-Notebook-footer {
-  /* TODO: re-enable */
-  display: none;
   width: 100%;
   margin-left: unset;
   background: unset;