Resolve "Update copyright"

Closes #160

See merge request !189

Merge branch '115-person-overview-implement-multiple-selection-for-marking-absences-as-excused-or-for-deleting' into 'master'

Resolve "[Person overview] Implement multiple selection for marking absences as excused or for deleting"

Closes #121 und #115

See merge request !111

Merge branch '157-permission-checking-decorators-raise-internal-server-error-if-the-user-is-anonymous' into 'master'

Resolve "Permission checking decorators raise internal server error if the user is anonymous"

Closes #157

See merge request !188

Resolve "Add page "Missing entries""

Closes #156

See merge request !183

Optimize ORM workload for week view by avoiding/minimizing prefetch operations

See merge request !173

Merge branch 'master' into 115-person-overview-implement-multiple-selection-for-marking-absences-as-excused-or-for-deleting

Resolve "[My students] Students lists aren't sorted alphabetically"

Closes #154

See merge request !181

Merge branch 'master' into 115-person-overview-implement-multiple-selection-for-marking-absences-as-excused-or-for-deleting