title: Issue while running interactive GUI with xlwings
body: <p>I have built a GUI (with PyQt5) which allow me to read an CSV, made some basic actions and send it to Excel.</p>
  
  <p>Then, I integrated this GUI into Excel using xlwings but I have a problem. When I am using the GUI, I can't manipulate the data in Excel. I assume it's because my macro is still running. </p>
  
  <p>Is there a way to run my GUI without loosing control of Excel ?</p>
  
  <pre><code>def Main():
      import sys
      app = QtWidgets.QApplication(sys.argv)
      MainWindow = QtWidgets.QMainWindow()
      ui = Ui_MainWindow()
      ui.setupUi(MainWindow)
      MainWindow.show()
      sys.exit(app.exec_())
  </code></pre>
  
  <p>and in Excel :</p>
  
  <pre><code>Sub GUI()
      RunPython ("import UImainwindow; UImainwindow.Main())
  End sub
  </code></pre>