title: selectText of NSTextField on focus
body: <p>Could anybody suggest a method to select all the text of an <code>NSTextField</code> when the user clicks it?</p>
  
  <p>I did find suggestions to subclass <code>NSTextField</code> and then use <code>mouseDown</code> or <code>firstResponder</code>,` but it's beyond my skill for now. So I was hoping either there would be an easier solution or somebody might be kind enough to detail the steps required.</p>