title: Using overlayVisible property in primeNg dropdown
body: <p>PrimeNG multiselect widget has overlayVisible property which makes the multiselect panel visible when widget is loaded.
  but PrimeNG dropdown doesn't have such property to enable the panel open by default.</p>
  
  <p>Any idea how it can be done?? Tried using few options like panelStyleClass and setting the panel style on dropdown's focus event but didn't work.</p>