ConfigIF: Improved top menu filtering.

The "Sites" tab is now shown even for users without the "View Settings"
privilege, if they have access to any of the sites.

The "Docs" tab is now hidden if there are no docs in the server.

Fixes [bug 6574].
Merge branch 'patches/bug6574' into devel

* patches/bug6574:
  ConfigIF: Improved top menu filtering.