title: catching dismiss event ngx-bootstrap modal
body: <p>I'm using angular 6 and ngx-bootstrap 3.0.1</p>
  <p>I display a modal and I want to be able to show a discard/cancel confirmation when the user try to close the modal after updating the form.</p>
  <p>I have no issue when the user use my custom close button, but I don't know how to call my closing function when he use the backdrop-click outside the modal.</p>
  <p>How can I handle the backdrop-click cleanly to be able to display my confirmation message?</p>