add support for extended addressing (xep-0033)

[bartekgorny]

You may want to add some syntactic sugar, depends on your taste - for now the interface is a bit raw, you have to pass a tuple containing multicast host and a list of #extaddress{} records.

[michalwski]

Did you try it with current MongooseIM tests? escalus_stanza:message/4 was modified, there is a good chance this function is used somewhere in big_tests. It be good to know that tests still work with your changes.

Please rebase this branch on top of current master (there was quite many changes in escalus recently) and open a PR in MongooseIM with escalus from this branch.

[NelsonVides]

Reviving this one, old and with some conflicts by now but I like the idea, would be cool to implement so in MongooseIM as well so having the testing tool will be useful beforehand. Any thoughts on this? @bartekgorny

[arcusfelis]

Not closing, because @NelsonVides is interested in it...