This custom version will add internally a constraint activities not overlapping for each pair of activities
with the same subject and which don't have the same activity tags.

Also, for activities having the same students there is an internally added constraint min 1 days between activities, 100%.

Requested by Peter B., 2018-11-18. Updated on 2021-08-15.

2022-09-15: The students' time horizontal timetable is 'compressed'.
