title: expand the bootstrap navbar when clicks a drop-down menu occurs
body: <p>Hello I want to know if it was possible to expand the bootstrap navbar when I click on a dropdown menu ? please</p>
  
  <p>before click:</p>
  
  <pre>
  +------------------------------------------------+
  |    THE NAVBAR -               dropdown menu \/ |
  +------------------------------------------------+
  </pre>
  
  <p>after click:</p>
  
  <pre>
  +------------------------------------------------+
  |    THE NAVBAR -               dropdown menu \/ |
  |                                     submenu    |
  +------------------------------------------------+
  </pre>