Resolve "GraphQLError: 'NoneType' object has no attribute 'id'"

Closes #323

See merge request !432

Merge branch '321-notfoundinregistry-no-such-preference-in-globalpreferenceregistry-with-section-alsijil-and-name' into 'master'

Resolve "NotFoundInRegistry: No such preference in GlobalPreferenceRegistry with section=alsijil and name=inherit_privileges_f..."

Closes #321

See merge request !431

Reformat and remove any_documentation predicate

See merge request !430

Resolve "Make permission check for coursebook route faster"

Closes #318

See merge request !428

Optimize query

See merge request !427

Fix data checks for new models

See merge request !425

Resolve "Add links to group/person detail pages in Core"

Closes #313

See merge request !419

Resolve "Missing Prop Participations on tardiness-field"

Closes #315

See merge request !424

Do release 4.0.0.dev7

See merge request !423

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

Bump version to 4.0.0.dev6

See merge request !416

Reformat

See merge request !415