title: Replace all tab operations with inserting four spaces in QPlainTextEdit widget
body: <p>I've got a QPlainTextEdit object which I'm using as a mini-python editor in one of my tools. The problem is that when you insert a tab in QPlainTextEdit, it inserts a great big tab rather than four spaces like I'd prefer.</p>
  
  <p>Is there a way to override this functionality, like you can in programs like Notepad++?</p>