Add management of tardinesses

Tardinesses of students, linked to documentations, have to be saved in some way (linked to absences?) and also be manageable in the frontend, ideally in the same places used to manage absences.

changed milestone to /AlekSIS%"[NLnet #3] Implement support for absences"

added part::frontend type::feature workflow::discussing labels

assigned to @ZugBahnHof

changed milestone to /AlekSIS%"[NLnet #3] Implement support for personal notes"

mentioned in merge request !362 (merged)

closed with commit b6f6eaf0

mentioned in commit b6f6eaf0

mentioned in commit 7522b1ef