patch review for the sortable_element helper

This patch adds the ability to call the sortable_element helper
without the :url parameter. This can be useful if you want to handle
the order update yourself and avoid calls to a remote action each time
the sort order changes. Example:

<%= sortable_element("my_list", :handle => "my_handle" ) %>

If you try to do something like this in the edge version it won't work
but used to in 1.2.X.

Looking for advice or +1 :slight_smile: