Refactoring: rename covid19 to flask_covid19

src/flask_covid19/__init__.py

src/flask_covid19/blueprints/app_admin/app_admin_views.py

src/flask_covid19/blueprints/app_all/all_views.py

src/flask_covid19/blueprints/divi/divi_test_views.py

src/flask_covid19/blueprints/divi/divi_views.py

src/flask_covid19/blueprints/ecdc/ecdc_test_views.py

src/flask_covid19/blueprints/ecdc/ecdc_views.py

src/flask_covid19/blueprints/owid/owid_test_views.py

src/flask_covid19/blueprints/owid/owid_views.py

src/flask_covid19/blueprints/rki_cases/rki_test_views.py

src/flask_covid19/blueprints/rki_cases/rki_views.py

...vid19/blueprints/rki_vaccination/rki_vaccination_views.py

src/flask_covid19/blueprints/who/who_test_views.py

src/flask_covid19/blueprints/who/who_views.py