[STORY - Quick_Win] LPS-35255 Display message in Navigation Configuration Preview when no navigation is available.

Hi Julio,

Originally, I made these changes to fix http://issues.liferay.com/browse/LPS-34828. 

Though, Byran has found a more simple solution (AUI-894), and he opened this new story http://issues.liferay.com/browse/LPS-35255, because he considered my changes as improvements instead of bugfix.

So, I rebased the source to master & here I'm sending a new pull to you, as you are one of the leads of Navigation portlet.

If you're getting "You do not have the Role to..." error message upon opening the Conf. panel, it's not because of my changes. To test the new behavior, just create a new Site & place Navigation portlet on the Home page of the new site.

Could you please review my changes & let me know if it meets your and the PM's requirements (or if you've any concerns)?

BTW, my changes touch only the Configuration action of Navigation portlet. Could you tell me why we display an empty navigation (in some cased) in general?

Many thanks,
Tibor