ComboBox autocompletion timer

Combobox items can be selected by pressing the first letters within a short period of time. After this delay, the lookup restarts.

For instance, pressing "par" will select "paris", but "pa (pause) r" will select "paris" and then "roma". The delay is by default 400 ms, and the new style attribute completionTimeout allows to configure it.

This style attribute also applies to RadioGroups.