groups api endpoint

src/groups/__init__.py

src/groups/admin.py

src/groups/apps.py

src/groups/migrations/__init__.py

src/groups/models.py

src/groups/serializers.py

src/groups/tests.py

src/groups/urls.py

src/groups/views.py

src/kszkepzes/settings/base.py

src/kszkepzes/urls.py