Add carry over feature for lessons and supervisions

The following discussion from !2 (merged) should be addressed:

• @yuha started a discussion: (+1 comment)

  TODO: Add carry over feature for lessons and supervisions.

changed title from Add carry over feature for lessons and supervisions. to Add carry over feature for lessons and supervisions

added part::backend part::frontend source::customer::engs type::feature labels

created branch 31-add-carry-over-feature-for-lessons-and-supervisions to address this issue

mentioned in merge request !25

changed milestone to /AlekSIS%"[NLnet #1 (closed)] Fix existing bugs with new timetable"