Improve human readable description of configured CRON expressions

[AFaust]

We currently include a human readable description generated from job CRON expressions as the cell title for the CRON expression cells in the Scheduled Jobs tool. This description is generated by using the cron-utils library. From some descriptions I have seen while preparing screenshots for the wiki documentation, there is some room for improvement (maybe warranting PRs to the cron-utils project). E.g. the CRON "0 0 0 ? 1 1 2030" currently results in the description text "at 00:00 at January month at Monday day at 2030 year" - which isn't wrong, just painfully weird/verbose.