Basic code cell splitting implemented.

IPython/frontend/html/notebook/static/js/menubar.js

@@ -70,6 +70,15 b' var IPython = (function (IPython) {'
         this.element.find('#delete_cell').click(function () {
             IPython.notebook.delete_cell();
         });
+        this.element.find('#split_cell').click(function () {
+            IPython.notebook.split_cell();
+        });
+        this.element.find('#merge_cell_above').click(function () {
+            IPython.notebook.merge_cell_above();
+        });
+        this.element.find('#merge_cell_below').click(function () {
+            IPython.notebook.merge_cell_below();
+        });
         this.element.find('#move_cell_up').click(function () {
             IPython.notebook.move_cell_up();
         });

IPython/frontend/html/notebook/templates/notebook.html

@@ -91,6 +91,10 b''
                 <li id="paste_cell_below" class="ui-state-disabled"><a href="#">Paste Below</a></li>
                 <li id="delete_cell"><a href="#">Delete</a></li>
                 <hr/>
+                <li id="split_cell"><a href="#">Split</a></li>
+                <li id="merge_cell_above"><a href="#">Merge Above</a></li>
+                <li id="merge_cell_below"><a href="#">Merge Below</a></li>
+                <hr/>
                 <li id="move_cell_up"><a href="#">Move Up</a></li>
                 <li id="move_cell_down"><a href="#">Move Down</a></li>
                 <hr/>