roster-view: add some delay before actually starting the live search
roster-view: add some delay before actually starting the live search

This avoid stacking a bunch of useless searches while user is typing as we
can't stop the old search before starting the new one.

https://bugzilla.gnome.org/show_bug.cgi?id=685278

GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets