Disconnect immediately when the app is put to sleep (or sent to background)

Closes QDS-14596

src/backend/dsconnector/ds.cpp

@@ -67,6 +67,12 @@ void DesignStudio::initPingPong()
             &QWebSocket::pong,
             this,
             [this](quint64 elapsedTime, const QByteArray &) {
+                if (elapsedTime > 1000)
+                    qWarning() << "Design Studio pong is too slow:" << elapsedTime
+                               << "ms. Newtork issue?";
+                else if (elapsedTime > 500)
+                    qWarning() << "Design Studio pong is slow:" << elapsedTime << "ms";
+
                 m_pongTimer.stop();
                 m_pingTimer.start();
             });