Also, add tests. One redis test fails, because the broker doesn't
implement things properly...

Infinitely repeating, by default, is not a good idea.

(it can create table on it's own, spawn tasks, clean up, perform aggregation)

This is better for timeouts, since it supports delays larger than ~30 minutes.

This uses PGMQ and a short-lived table with random name.

periodic task added to demo app

Demo: 'echo' job is archived

It is not well thought-out