Active State for PanelMenu sub menus.

[suraj021]

I am submitting a

[ ] bug report => Search github for a similar issue or PR before submitting
[x ] feature request => Please check if request is not on the roadmap already https://github.com/primefaces/primeng/wiki/Roadmap
[ ] support request => Please do not submit support request here, instead see http://forum.primefaces.org/viewforum.php?f=35

I am just recreating this issue again to bring it to the notice. This issue was already created but was not solved but closed #644.
It would be great if we have this feature in the next release.

[cagataycivici]

Added ui-state-active to the active submenus however with no default style as a design decision, still page authors may use "ui-state-active" class to apply styling.