Refactor auth_sasl_scram_sha1/2
Simplify escalus_stanza:auth / :auth_response and fix dialyzer warnings
Fix typo: undefiend -> undefined
Be a bit more lenient regarding exml version

There are some typespec fixes in the new version,
but no functioanlity/API changes.
Fix more escalus_stanza.erl type discrepancies
Typespec escalus_connection
Fix more bugs with non-lists as #xmlel.children