When fixing schedules, make sure that there is exactly one scheduled update for each available feed.
When fixing schedules, make sure that there is exactly one scheduled update for each available feed.

FixSchedulesWorker now not only adds missing scheduled updates. It also counts how many times are updates scheduled for each available feed. If any feed is found to have more than one scheduled update, this is considered an error. All scheduled updates for that feed are removed, and a new scheduled update based on its last_fetched and fetch_interval attributes is set.

amatriain/feedbunch,amatriain/feedbunch,jmwenda/feedbunch,amatriain/feedbunch,jmwenda/feedbunch,jmwenda/feedbunch,amatriain/feedbunch