Need a GUI way to update system-wide GDM settings for extended desktop instead of clone mode

This is a related problem to #148189. It's kind of hard to pin down which package this should be submitted under as it is somewhat of a systemic problem between the xorg intel driver, gdm and the per-user screen resolution configuration GUI.

For the record, I'm running Jaunty with
xserver-xorg 7.4~5ubuntu16
xserver-xorg-core 1.6.0-0ubuntu4
xserver-xorg-video-intel 2:2.6.3-0ubuntu2
gdm 2.20.10-0ubuntu1
gnome-control-center 1:2.26.0-0ubuntu1

This is the way I understand it:
When xorg starts, the intel driver will currently detect available screens and activate all of them as duplicates (all the same resolution). This is probably better behaviour than described in #148189, but it still looks like a train wreck if you have multiple LCDs that require different resolutions.

I admit it might be difficult to improve the default duplication behaviour. Currently, if you duplicate the displays with native resolution (by setting up xorg.con manually), GDM defaults to having the greeter span the largest monitor and being cut off in the smaller ones. Alternatively, due to limitations in the Intel graphics chipsets, defaulting to native resolution xinerama is not an option because this may require expanding the virtual screen to a size larger than will allow 3d acceleration. This of course is not to mention the issue of determining the "correct" xinerama layout.

Fine, imagine I'm a new user who just installed Ubuntu and I know nothing about editing config files. I am appalled by the default screen layout when GDM pops up, so when I log in, I find the Display settings GUI and fix it to what ever settings I want (including making a larger virtual screen - kudos BTW!). These settings will persist across logins of that user *and only that user*. Notably, GDM will still has the same awful defaults. Short of editing xorg.conf there does not appear to be a way to get GDM to behave sanely.

I might thus make two concluding suggestions:
1) Make the intel driver default to screen duplication *at native resolution* AND have GDM default to spanning the smallest screen rather than the largest one as it does now.
2) Allow users to configure the default GDM display settings through the Display settings GUI. I imagine this could be achieved by having GDM call xrandr during startup.