UI support for "every nth" minute

[AhsanAyaz]

This is inspired from #54. But that is a HUGE effort to do as it requires possible implementation of all existing options (hours, minutes, days, weeks). Also, with a lot more complex situations.
But every nth minute is probably a good start in the direction suggested in #54 .
So it would be nice to implement it alongside the "Minute" selection. It can be every minute. Or every 5th minute etc.

[lovelldies]

Thanks for looking into this @AhsanAyaz !