New autocomplete widget

Task #5009

This new autocomplete widget (the one used in the search bar) does not do remote calls automatically, but on demand.  In theory, it should lead to a better user experience, not having the ui blocked every time long remote calls are done.

It also has the benefits of bringing us one step closer to not depend on jquery.ui.  Bonus point: the code is quite short (< 200 loc i believe)