handle XEP-191 (blocking command) in a better way: hability to block a contact when server doesn't support privacy lists, add / remove jid to blocked list only when we get the result from server, handle blocked / unblocked contacts by other resources

This will make Gajim start a bit faster and more entropy can be
generated for key generation.

Fixes #7735.

Jingle File Transfers work without Farstream.

ICE-UDP transport is also implemented as a part of Farstream (libnice)

Fixes #7713

Fixes #7671

fix double iq-result sending

signature algorithm for old pyOpenSSL.

Fixes #7641

The prime is: 2^4096 - 2^4032 - 1 + 2^64 * { [2^3966 pi] + 240904 }

RFC3526 specifies a generator of 2.

The generation of the group is described in RFC 2412.

Fixes: #7644

Fixes: #7642

Fixes: #7642

More on the effect of TLS tickets:
https://media.blackhat.com/us-13/US-13-Daigniere-TLS-Secrets-Slides.pdf

Fixes #7638

add configuration option tls_version

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