[simple_link]: Support for :icon added.

If :icon is specified, then its ok for :for => blank
But one or the other (:icon, :for or both) must be specified

:icon => sth will add an <i class='sth'></i>
[notification]: First attempt at standardizing interface for showing AJAX responses

Got a bell in the control panel that drops down to show messages from the server
The bell is fixed.
The JSON expected is fixed