irc: hide passwords in commands or messages sent to nickserv with modifiers (bug #38346)

New modifiers: "irc_command_auth" and "irc_message_auth".
Option removed: irc.look.hide_nickserv_pwd
New option: irc.look.nicks_hide_password
rmodifier: rename default rmodifier "nickserv" to "command_auth" (with new modifier "irc_command_auth"), add default rmodifier "message_auth" (modifier "irc_message_auth")