gui/cli: unify and improve event exit code reporting #74

Instead of "(exited with N)" show "('EVENT_NAME' exited with N)".
Factor out the code which generates tese messages.

v2: mark all messages for translation.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Jiri Moskovcak <jmoskovc@redhat.com>