Bug 1025779 - Generation (at POST /call-url)  and retrieval (GET /calls/{token}) of the call-url should require/provide an optional issuer parameter

We don't have body.issuer in the specification: https://wiki.mozilla.org/Loop/Architecture/MVP#POST_.2Fcalls

We have to be careful about the naming there because caller and callee are reversed in case of direct calls and there is no call-url issuer in case of direct call.

It is one more reason to be careful about the issuer wording. Are we talking about the `caller Id/Friendly name` or `callee Id/Firendly name` there?