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.

After the random number generator seed file is read overwrite the
previous content of the file.

Jingle File Transfers work without Farstream.

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

Fixes #7713