Refactoring: rename covid19 to flask_covid19

src/flask_covid19/__init__.py

src/flask_covid19/blueprints/app_all/all_service.py

src/flask_covid19/blueprints/app_mq/application_workers.py

src/flask_covid19/blueprints/app_web/web_service.py

src/flask_covid19/blueprints/app_web/web_services.py

src/flask_covid19/blueprints/divi/divi_test_service.py

src/flask_covid19/blueprints/ecdc/ecdc_test_service.py

src/flask_covid19/blueprints/owid/owid_test_service.py

src/flask_covid19/blueprints/rki_cases/rki_service.py

src/flask_covid19/blueprints/rki_cases/rki_service_import.py

src/flask_covid19/blueprints/rki_cases/rki_service_update.py

src/flask_covid19/blueprints/rki_cases/rki_test_service.py

src/flask_covid19/blueprints/who/who_test_service.py