Move image and PDF import tasks to arkindex-tasks

arkindex/dataimport/git.py

arkindex/dataimport/management/commands/import.py

arkindex/dataimport/models.py

arkindex/dataimport/tasks/__init__.py

arkindex/dataimport/tasks/base.py

arkindex/dataimport/tasks/image.py

arkindex/dataimport/tasks/pdf.py

arkindex/dataimport/tests/test_image.py

arkindex/dataimport/tests/test_pdf.py

arkindex/dataimport/tests/test_tasks.py

arkindex/project/checks.py

arkindex/project/settings.py

arkindex/project/tests/test_checks.py

base/Dockerfile

requirements.txt