Extracts the "Grant role" member picker's typeahead combobox into a
reusable static/js/searchable-select.js (opt in via data-searchable on
the widget), and reuses it for the news form's teams field -- a proper
multiselect with removable pills and filter-as-you-type, replacing the
plain checkbox list. Needed forwarding widget attrs through the shared
select template, which never passed them to the rendered <select>.
Bernard Siebens
d9b4337319