Scheduler improvements

[Andrew]

Could you please add "day of week" settings for scheduler task?

[support]

We plan to switch to a CRON-like version of the scheduler, which will specify any event variants instead of fixed intervals. We face two problems here - we need to ensure compatibility with the old scheduler and make the editing of CRON parameters more user-friendly. I suspect that not all users will want to learn the settings as a series of numbers instead of the usual date/time.