Set a start date for dripping courses

Dripping is from date of sign-up. There is no option to set a start date. This means, it will not work for cohorts, only on-demand "evergreen" courses. It requires manually scheduling every lesson, sometimes over a number of weeks.

Case study: I ended up manually scheduling each of 75 lessons of a daily challenge over 6 weeks. Then I had to create a parallel schedule in threads and post there at the same time, so that the community discussion cards from the course had a counterpart participants could actually leave comments on. No integrated calendar, no automated recurring schedule. Big frustration. I probably spent six days just doing this.

Related:

https://heartbeat.canny.io/feature-requests/p/one-heartbeat-calendar-for-scheduling-courses-threads-and-events

https://heartbeat.canny.io/feature-requests/p/improve-scheduling-interface-function