Don't raise any celery task on feed status error. Instead, self.error().

Raising the task just clutters the queue again and again, in case of a
persisting network error. As the error could be persistent, use self.error()
like any other feed error. But in case the error is temporary, update
{date_}last_fetch to re-refresh after the fetch_interval, this will make
us get more that one minute between the 2 refreshes.
version bump for 0.80.44.
Merge branch 'release/0.80.44' into develop