Add SuccessNextMixin for automatic redirecting after finishing an action

See merge request !471

Some JS and CSS were added, too.

Add template for pull requests at GitHub for mirroring

See merge request !472

Resolve "Add possibility to upload files via CKEditor"

Closes #364

See merge request !470

Resolve "Provide landscape print template"

Closes #311

See merge request !469

Update poetry.lock

See merge request !466

Merge branch '333-add-possibility-to-manage-object-level-permissions-for-group-and-person-models-in-admin' into 'master'

Resolve "Add possibility to manage object-level permissions for Group and Person models in admin interface"

Closes #333

See merge request !418

Include support for icons in Materialize chips template

See merge request !462

Resolve "CSS arrows for django-tables2 materialize"

Closes #358

See merge request !465

Make help text in Materialize forms smaller

See merge request !463

Resolve "Add own menu entry for notifications"

Closes #327

See merge request !447

Bugfix/do not link person if anonymous

See merge request !461

Always return False for `has_person` if not logged in

See merge request !460

Revert "Support custom authentication backends"

Closes #313

See merge request !459

Enable all panels in djdt

See merge request !458

Resolve "Allow automatic linking of persons to account by e-mail address"

Closes #332

See merge request !414

Update tox.ini; compile messages before building dist

See merge request !457

Support `to_python` on fake proxy field

See merge request !456