Searching across NoDisplay desktop items can produce weird
results to the user (including duplicates, and items that
aren't really applications at all.) So, don't include them
normally.
But continue including NoDisplay items when we look up the
desktop file for a window, since we want to catch applications
like Evince and Nautilus which are otherwise NoDisplay.
http://bugzilla.gnome.org/show_bug.cgi?id=587548
Add a GConf key for favorites, and API for retrieving them.
Also add shell_app_system_lookup_basename, which we use from
the app monitor to look up WM_CLASS ids.
To avoid loading applications from two different systems, use
ShellAppSystem solely. This unifies the initial load and the
reload.
Extend ShellAppSystem to also load settings/preferences, and
ensure they appear in the search.
