qml: uncomment DebugMessageHandler install

DebugMessageHandler is needed to route output to debug.log and
should not have been commented out.

src/qt/bitcoin.cpp

@@ -622,7 +622,7 @@ int GuiMain(int argc, char* argv[])
     qApp->installNativeEventFilter(new WinShutdownMonitor());
 #endif
     // Install qDebug() message handler to route to debug.log
-    //qInstallMessageHandler(DebugMessageHandler);
+    qInstallMessageHandler(DebugMessageHandler);
     // Allow parameter interaction before we create the options model
     app.parameterSetup();
     GUIUtil::LogQtInfo();