title: binding to angular strap datepicker events when they get triggered
body: <p>I'm using angular strap datepicker and I want to execute some of my own logic when the datepicker opens up and closes.</p>
  
  <p>How can I recognize these events inside my controller, and bind to them?</p>
  
  <p>and not just to the datepicker events, but any of angular straps events for that matter. </p>
  
  <p>An example of what I want to do:</p>
  
  <p><a href="http://plnkr.co/edit/Uy1Lz6I0NWSACV4kyljk?p=catalogue" rel="nofollow">http://plnkr.co/edit/Uy1Lz6I0NWSACV4kyljk?p=catalogue</a></p>