Update sub repos 2021 10 06

This MR switches to the latest versions of the sub repos (frontend, backend, sms-cv). It tries to integrate all the changes for the env variables and is another approach to handle static files with urls like /static/backend and /static/cv - without the need for a more specialized nginx image for the local docker-compose.

It will also reflect the change to switch to the pkce flow instead of the implicit flow.