Update copyright information

See merge request !58

Merge branch '73-add-rules-and-permissions' of edugit.org:AlekSIS/official/AlekSIS-App-Alsijil into 73-add-rules-and-permissions

Merge branch '73-add-rules-and-permissions' of edugit.org:AlekSIS/official/AlekSIS-App-Alsijil into 73-add-rules-and-permissions

Merge branch '73-add-rules-and-permissions' of edugit.org:AlekSIS/official/AlekSIS-App-Alsijil into 73-add-rules-and-permissions

Resolve "[Lesson view] Show summary (homework, etc.) of previous lessons"

Closes #29

See merge request !57

Resolve "Use base_print.html for full register print out"

Closes #76

See merge request !55

- Add extra templates for absences and tardinesses
- Add model extensions for lesson documentation and personal notes to LessonPeriod

Fix wrong offsets for weekdays

See merge request !54

Resolve "[Lesson view] Show buttons to go the previous/next lesson"

Closes #83

See merge request !56

Reason: A too complex query can cause database problems.

Resolve "Show status icon for every lesson"

Closes #63

See merge request !50

Fix lint issues and reformat all files

See merge request !53

Week has to be annotated before querying teachers

Resolve "Fix aggregation of absences and tardninesses"

Closes #75

See merge request !52

Merge branch '73-add-rules-and-permissions' of edugit.org:AlekSIS/official/AlekSIS-App-Alsijil into 73-add-rules-and-permissions