RANDR - Add GConf options for a boot-time configuration

There are two boolean keys:
/apps/gnome_settings_daemon/xrandr/turn_on_external_monitors_at_startup
/apps/gnome_settings_daemon/xrandr/turn_on_laptop_monitor_at_startup

These can be tweaked by OEMs to select the default policy for
external monitors.

Signed-off-by: Federico Mena Quintero <federico@novell.com>