Display a "No activity" message if you don't have the right to see activity entries

If the wiki is empty:

• and you are a registered user you see:
  
• if you are unregistered you see:
  

But if there are entries in the Activity Stream, but you don't have the right to view them, the Activity Stream is displayed empty.

• you see as a registered user:
  
• you see as unregistrered:
  

We should take into consideration that we don't display entries because of rights and display an empty message instead.