Discussion of proposed design for careteam work

Available for review, but please don't merge yet.
In this "get received invitation" call:

- `GET /confirm/invitations/:userid` here `userid` is the logged in user, i.e. the "receiver" correct?
- In the return body, `userid: 123abc` is also the *receiver* (as well as the `email`), right?
- I would be missing the *sender*'s id, so I can display "Mary Smith wants to share her data with you" (the sender here is "Mary Smith"). I'm calling it `from: 456` for now, feel free to suggest another attribute name