This adds the following API:
* cc_display_config_get_ui_sorted_monitors
Returns the monitors in UI order
* cc_display_config_count_useful_monitors
Counts the useful monitors (active and usable)
* cc_display_monitor_is_useful
Checks if a monitor is active and usable
* cc_display_monitor_is_useable
Check if a monitor is marked as useable
* cc_display_monitor_set_usable
Used to mark builtin monitors as unusable if the lid is closed
* cc_display_monitor_get_ui_*
Get the UI number and strings for display
https://bugzilla.gnome.org/show_bug.cgi?id=786971
This will allow us to switch the display panel away from using the
GnomeRR api directly in order to gracefully move to a new DBus display
configuration API to be provided by mutter while still keeping the
existing functionality on top of the GnomeRR api while the new one
is developed.
https://bugzilla.gnome.org/show_bug.cgi?id=782785