Implement part and join, both ways

src/bridge/bridge.hpp

@@ -32,6 +32,7 @@ public:
 
   void join_irc_channel(const Iid& iid, const std::string& username);
   void send_channel_message(const Iid& iid, const std::string& body);
+  void leave_irc_channel(Iid&& iid, std::string&& status_message);
 
   /***
    **
@@ -60,6 +61,11 @@ public:
    * Send a MUC message from some participant
    */
   void send_muc_message(const Iid& iid, const std::string& nick, const std::string& body);
+  /**
+   * Send an unavailable presence from this participant
+   */
+  void send_muc_leave(Iid&& iid, std::string&& nick, std::string&& message, const bool self);
+
 private:
   /**
    * Returns the client for the given hostname, create one (and use the