notification: transmit originating trigger as part of evaluation

Transmit the full trigger object instead of its condition when sending a
notification to a client. This allows clients to reliably filter on
triggers as, currently, only the name of a trigger is made available to
clients as part of the "on_event" evaluation object (the owner uid is
needed to perform a correct comparison for filtering).

This will also make the trigger accessible for all condition types.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I61d587436177eb34744487a1d3c486d87fe2e1f1