Resolve "Add missing __str__ methods"

Closes #275

See merge request AlekSIS/official/AlekSIS!316

Resolve "Let apps add extra permissions to models"

Closes #273

See merge request AlekSIS/official/AlekSIS!308

Resolve "Create / delete person and group"

Closes #242

See merge request AlekSIS!265

Resolve "Implement django-health-check"

Closes #133

See merge request AlekSIS/official/AlekSIS!315

Resolve "Fix design of custom error pages"

Closes #292

See merge request AlekSIS/official/AlekSIS!311

Fix paths to core templates in some templates

See merge request AlekSIS/official/AlekSIS!312

Fix and extend base_print.html

See merge request AlekSIS/official/AlekSIS!313

Revert "Merge branch '133-implement-django-health-check' into 'master'"

See merge request AlekSIS/official/AlekSIS!314

This reverts merge request !261

Resolve "Implement django-health-check"

Closes #133

See merge request AlekSIS!261

Fix paths to language form template

See merge request AlekSIS/official/AlekSIS!310

Add method to inject permissions to ExtensibleModels dynamically

Resolve "Link data to school term"

Closes #40

See merge request AlekSIS/official/AlekSIS!299

Resolve "Dropdown for languages"

Closes #265

See merge request AlekSIS/official/AlekSIS!295

Add universally usable progress bar for Celery tasks

Closes #287

See merge request AlekSIS/official/AlekSIS!304

Resolve "Show guardians and children on person view"

Closes #288

See merge request AlekSIS/official/AlekSIS!307