sorting happens in python now - since only this solution is compatible
with prefetch

Is used in person_overview & coursebook.

The previous filtering result for participations did not survive the
annotations done by annotate_person_statistics_for_school_term.

& reintroduce some abbreviations.

It's now reachable under coursebook/print/group/id

django.po still needs adjusting

django.po still needs adjusting

This reverts commit b3c63074.

Do release 4.0.0.dev6

See merge request !421

Update changelog

See merge request !420

Migration path to new models

See merge request !396

Resolve "Documentation dialog should be persistent if dirty"

Closes #286

See merge request !418

Resolve "Creating absence fails / absence reasons do not load"

Closes #311

See merge request !417