Refactoring: rename covid19 to flask_covid19

src/flask_covid19/blueprints/data_divi/divi_views.py

...vid19/blueprints/data_divi/templates/divi/divi_tasks.html

src/flask_covid19/blueprints/data_ecdc/ecdc_service.py

src/flask_covid19/blueprints/data_ecdc/ecdc_views.py

src/flask_covid19/blueprints/data_owid/owid_views.py

src/flask_covid19/blueprints/data_rki_cases/rki_views.py

...19/blueprints/data_rki_cases/templates/rki/rki_tasks.html

src/flask_covid19/blueprints/data_who/who_views.py