Logs every hour

[edemaine]

To deal with this issue and in general be able to detect that someone was in a meeting during a time interval but didn't change anything during that interval, we should log the current value of each presence every hour. I think this would be quite small. To avoid too much load at a single moment, each presence could have a random hour timer, or just one hour from when they joined. New type of presencePulse with no diffs.