New "conference" API replacing old "group" API

[iphydf]

In https://github.com/TokTok/c-toxcore we have made old group chats a first class supported API and rebranded it as conference. The new group chats will be called "group". We have also removed user data from callback registration functions. This now needs to be passed to tox_iterate.

[codedust]

:+1: Thanks for the great work! I implmented the changes in the Tox API, group chats will follow when I have more time. Will there be a difference between the currently existing conferences and the new group chats?

EDIT: In other words: Will the conferences be of any use after the new group chats are implemented?

[SergeyDjam]

Whether there are plans of implementation of group chats?

[codedust]

I'm currently not planning to add support for group chats in the near future if there's not a great need for it since there's an open PR at the c-toxcore repo that will redesign the groupchat API: https://github.com/TokTok/c-toxcore/pull/135