Add support for offline mode

It should be possible to request a session, which can be used offline. This is helpful for situations where no reliable internet connection is available, for example in the train.

- Access to TeamForCapella will not be possible from offline sessions.
- It should be possible to run the session on Linux, macOS and Windows devices.
- There should be a framework with instructions to run a docker container. The docker container should be exposed via RDP or direct X11 Forwarding.
- The workspace will not be synced with the server. There will be a different local workspace (Docker named volume).