Rename iq_responder_callback_t to irc_… and add the equivalent to wait for iqs
Implement PING, user to user only (XMPP and IRC side, using CTCP PING)

ref #2757
Add utils::revstr
Implement PING to in-room participant

ref #2575
send_iq_result can have a "from" with just the domain name
Implement the PING on a server or the gateway itself

fix #2575