Follow-up from "Resolve "Reimplement notification system on base of new calendar system""

The following discussion from !360 (merged) should be addressed:

• @yuha started a discussion:

  TODO: Also create alarms when substitution is deleted (how? idk)

changed milestone to /AlekSIS%"[NLnet #1 (closed)] Implement timetable notifications"

added part::backend type::feature labels

assigned to @yuha