Add some basic form field and widget to manage autocompletion.
AutocompleteModelChoiceField inherits from ModelChoiceField and had a 'site' parameter which can be an AdminSite
instance to provide a FK lookup using admin's change_list view.
Its default widget is AutocompleteWidget which inherits from HiddenInput but isn't hidden. The input receive 2 extra
attrs (search_url and lookup_url).
Basic test of the AutocompleteModelChoiceField in project test.
Basic test of the AutocompleteModelChoiceField in project test.