color: adapt to GnomeRR API changes

GnomeRR no longer exposes disconnected outputs, so we don't need
to filter them ourselves.

https://bugzilla.gnome.org/show_bug.cgi?id=705507
power: adapt to GnomeRR API changes

Reading the backlight from GnomeRR can't fail anymore (although
-1 can be returned, meaning that XBACKLIGHT is not supported).
Also, for GnomeRR the value is always a percentage.

We still need to handle min/max in case we use sysfs directly
(which will be the common case when we move to wayland)

https://bugzilla.gnome.org/show_bug.cgi?id=705507
wacom: adapt to GnomeRR API changes

GnomeRR now returns the EDID IDs as strings directly, so we don't
need to convert them to compare to the settings. Also, we don't
need to filter disconnected outputs, it's done by mutter now.

https://bugzilla.gnome.org/show_bug.cgi?id=705507
xrandr: remove ApplyConfiguration DBus method

In the new model, the client that wants to change the display
configuration asks mutter for the new layout directly, and that
takes care of saving to monitors.xml or restoring the existing
configuration if the new one fails.

https://bugzilla.gnome.org/show_bug.cgi?id=705507
xrandr: adapt to the new model for display configuration

Stop handling monitors.xml and the initial modeset for the session,
as well as monitor hotplug and lid switches. All that is implemented
in mutter now.
What is left in the xrandr plugin is Fn-F7 (for lack of a better
place) and Rotate. Both will go in mutter/gnome-shell at some point.

https://bugzilla.gnome.org/show_bug.cgi?id=705507
power: restore the ability of running the test suite

We need to provide a mock mutter in the test environment.
Also, we need to make sure a few objects exist right away, as
the mock environment starts dbus calls before we're really
initialized.

https://bugzilla.gnome.org/show_bug.cgi?id=705507