Swivel-VPNs without Swivel \o/

General workflow:

1) Run `hsrvpn-getsecret` to obtain a secret based on the rollout email.
   Alternatively, obtain it via mitmproxy from the phone app, and run:
   `keyring set hsrvpn-gettokens <username>` to set it.

2) Run `hsrvpn-gettokens <username>` to get 100 tokens based on the secret.

3) Use `keyring set openhsr-connect <username>` to set your HSR password
   (unless you use OpenHSR connect already).

4) Run `hsrvpn <username>` to connect, or `hsrvpn-showtoken <username>` to
   show a single token.