Fix motion closed notifications

@robguthrie this fixes the motion_closed notifications that you accidentally broke while you were fixing the notifications.

Not sure if you realised it, but those specs you commented out were actually legitimate failures.

All sorted now though. I've made the notification template a little bit more object-oriented. And also we've now got cukes for the notifications, which I think is going to be a good pattern for us in the future so that we can test all our notification logic in one place.