fix double iq-result sending

signature algorithm for old pyOpenSSL.

Fixes #7641

add configuration option tls_version

Related to
https://python-nbxmpp.gajim.org/ticket/17

http://tidy.sourceforge.net/

Fixes #7628

force sending muc invitation to the jid/resource if we're chatting with a specific resource. Fixes #7582

add a <private> element to message stanza when message carbons is enabled and message is encrypted. Fixes #7616

Fixes #7662

http://docs.python.org/3/library/logging.html

  Note: There is an obsolete method warn which is functionally identical to
  warning. As warn is deprecated, please do not use it - use warning instead.