p-dropdown: add a class to the ui-dropdown element if open

[me-12]

I would like to add a different style to the .ui-dropdown element if the dropdown is open. Currently there is no way to tell if the dropdown is opened or not. A solution would be to add a class like ui-dropdown-open to the .ui-dropdown element if the dropdown is opened.

[Mrtcndkn]

When you opened the dropdown panel ui-state-focus is added to the component the sameway when you close it ui-state-focus is still there.Maybe you can style the focus?

[cagataycivici]

I've added "ui-dropdown-open" to the main outmost div container element. It is removed when dropdown is hidden.