Discussion of proposed design for careteam work

Available for review, but please don't merge yet.
This comment is both for "dismiss" and "accept" received invitation.

- Should the URL be `/confirm/dismiss/invitations/:userid/:invited_by`, to be consistent with the `GET /confirm/invitations`?
- The comment that no body is required because "it's a PUT" is a little misleading to me, because in my mind a PUT is an "update" and can contain a body?