Enable Ajax and Instant search for Top Menu Module

Following the instructions reported by Nemo (http://nemops.com/ajax-instant-search-prestashop-top-menu/#.U1jIiHV0zgg) and under his permission I've added the possibility to have the autocomplete and eventually the instant search for the search bar in the top menu.

I've only modified the core tpl of the module and not the one in the theme along with the core blocktopmenu.php.

For every information or request please don't hesitate to contact me.