Rewrite the whole IID usage

IRC users and channels are now distinguished by the separator used in the
IID (% or !).

ref #2468

src/xmpp/xmpp_component.hpp

@@ -130,6 +130,12 @@ public:
   void send_invalid_room_error(const std::string& muc_jid,
                                const std::string& nick,
                                const std::string& to);
+  /**
+   * Send an error to indicate that the user tried to send a message to an
+   * invalid user.
+   */
+  void send_invalid_user_error(const std::string& user_name,
+                               const std::string& to);
   /**
    * Send the MUC topic to the user
    */
@@ -141,7 +147,7 @@ public:
   /**
    * Send an unavailable presence for this nick
    */
-  void send_muc_leave(std::string&& muc_name, std::string&& nick, Xmpp::body&& message, const std::string& jid_to, const bool self);
+  void send_muc_leave(const std::string& muc_name, std::string&& nick, Xmpp::body&& message, const std::string& jid_to, const bool self);
   /**
    * Indicate that a participant changed his nick
    */