Is your feature request related to a problem? Please describe.

MaintainingJobQueue is not easy and sometimes error prone, see e.g.#1338

Describe the solution you'd like

We could refactorJobQueue to use a third party library for the scheduling, keeping therun_* methods as wrappers. We should probably also add arun_cron as suggested in#1337 as convenience wrapper for all the other cases we can't all cover (like run a job every time mars and saturn align …)

Describe alternatives you've considered

Just implementrun_cron would be a first step.