Initial rough dialback support

* [x] <del>Code is rough</del> Greatly reduced oddness by `Node` module  and finding stream by ID.
* [x] <del>Storing secret probably in the wrong way</del> Finding stream by ID now seems sensible.
* [ ] No tests
* [ ] Stop offering SASL external if cert invalid
* [ ] Rebase into a clean commit
* [ ] No cluster support (Only if upstream interested?)
* [ ] Investigate also adding Bidi (XEP-0288) support  (Only if upstream interested?)
This checks whether the result was informing us that the verification done by the receiving server succeeded, if so we proceed to communicate on this outbound connection.