Remove dependency on `UserMeta` in `ChorusRequest`

[bitfl0wer]

Currently, ChorusRequest::send_request() relies on a user: ChorusUser. This is a problem, because there are cases where we'd like to send a rate-limited request without having a pre-existing ChorusUser struct. This is the case when logging in and registering an account on the API server. We currently use ChorusUser::shell() to give us a dummy ChorusUser to send the request with. However, this is a 'dirty' fix, which only gets dirtier as more things get added onto the ChorusUser struct. One idea for a solution would be to replace the requirement of ChorusUser with a trait, which defines methods to get all required information to send the request.