If we're typing we want to send composing. If we empty the entry we
want to send active. If we're typing but don't type any more for
COMPOSING_STOP_TIMEOUT seconds, we want to send paused. Simple.
This behaviour was stolen from Empathy where it has won many awards.
https://bugzilla.gnome.org/show_bug.cgi?id=650196
Based on patch from Jonny Lamb <jonnylamb@gnome.org>
Signed-off-by: Alban Crequy <alban.crequy@collabora.co.uk>