Merge branch 'master' into stable

CHANGELOG.md

taiga/__init__.py

taiga/auth/services.py

taiga/celery.py

taiga/deferred.py

taiga/github_hook/event_hooks.py

taiga/mdrender/service.py

taiga/projects/issues/serializers.py

taiga/projects/tasks/serializers.py

taiga/projects/userstories/models.py

taiga/projects/userstories/serializers.py

tests/integration/test_auth_api.py

tests/integration/test_github_hook.py

tests/integration/test_userstories.py