Irccd: do not own a queue in irc::connection class, closes #791 @1h Since the server is an automatic state machine that recreate a new session after a connection failure, we may have some invalid references in the irc::connection class if there are still handler running. Because server is already a std::shared_ptr that manages itself, it was heavy to do the same in irc::connection class. Therefore, the irc::connection class is now only responsible of connecting/receiving/sending data (and parsing it). Update the server class to use a send queue and allow the user sending command at any time which will be postponed once connected.