Expect a PONG response to our PINGs (#1476)

If no PONG was received, force a reconnection

Fixes #1164

src/providers/irc/IrcConnection2.hpp

@@ -18,6 +18,9 @@ private:
     QTimer pingTimer_;
     QTimer reconnectTimer_;
     std::atomic<bool> recentlyReceivedMessage_{true};
+
+    // waitingForPong_ is set to true when we send a PING message, and back to false when we receive the matching PONG response
+    std::atomic<bool> waitingForPong_{false};
 };
 
 }  // namespace chatterino