allow ignore_unknown_contacts, send_os_info and log_encrypted_sessions to be set per_account in ACE. Fixes #4730

ID will be autogenerated (like from): Done by dispatcher as it wraps transports send, when plugged into NonBlockingClient.

detection code

Introduce a get_instance factory method for all plugins and other xmpp related classes. This will help us to decouple plugs in order to make them testable.

Switch to SSL version 3 as the channel encryption protocol. As of http://docs.python.org/dev/library/ssl.html this is the maximally compatible SSL variant.