Drop gconf from the default installation

It seems we could finally get ride of libgconf2-4 users next cycle, looking on current quantal we still some users, including:

- gksu (can be replaced by pkexec)
- gnome-media (through libgnome-media-profile, we probably need to port that one)
- lightdm-remote-session-uccsconfigure (need to look at it but I guess it shouldn't be hard)
- update-notifier
- ubuntu-release-upgrader-gtk
- unity (for config migration purpose I guess)

That's a reasonable list to work through
Things I can see in that category:
- turn the "bluetooth indicator" (patch over fallback-session code from upstream) to a proper indicator
- turn the "keyboard indicator" (the code we patch is going away in GNOME 3.6) to a proper indicator
- deal with disk mounting in unity (we use the GNOME fallback-session code)

(It would be good to have design input on the indicator before we start if we are going to do that, if we rewrite them we can as well do it in a way which improves the design)

There are probably others things in that category but those are the main ones I can think about