title: QTableView: how to do something on start/end editing?
body: <p>Are there any signals (I cannot find anything in the docs) emitted when
  user starts and ends the <code>QTableView</code> widget cell edititing?</p>
  
  <p>I want to execute some function from table model then user begins edit eny cell and execute another function when user ends editing. How can I do this?</p>