timer: rate-limit the "timer expiry in the past" error messages

timer: rate-limit the "timer expiry in the past" error messages

We already ratelimit the normal notification about event processing
lagging behind but in the case of timers actually expiring late, we'd
pass those messages on. So lots of clicks on a slow-reponse system
resulted in lots of messages triggered by the debounce timers.

Use the same ratelimiting as the event processing warning, 5 messages
per hour which should be a good balance between warning and not spamming
the log.

Fixes #711

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>