Rework and consolidate monitor handling in MetaScreen

Consolidate all places that deal with output configuration in
MetaScreen, which gets it either from XRandR or from a dummy static configuration.
We still need to read the Xinerama config, even when running xwayland,
because we need the indices for _NET_WM_FULLSCREEN_MONITORS, but
now we do it only when needed.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
Split monitor handling into an helper object

Create a new singleton object, MetaMonitorManager, which deals
with reading the XRandR configuration and in the future applying
the new one.
This is required because xwayland will not bind the xserver interface
until he has seen the current wl_outputs, so we can't wait
until MetaScreen is built to expose them.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
Introduce a new DBus interface for display configuration

This new interface will be used by the control center and possibly
the settings daemon to configure the screens. It is designed to
resemble a simplified XRandR, while still exposing all the quirks
of the hardware, so that the panel can limit the user choices
appropriately.

To do so, MetaMonitorMode needs to track CRTCs, outputs and modes,
so the low level objects have been decoupled from the high-level
MetaMonitorInfo, which is used by core and API and offers a simplified
view of HW, that hides away the details of what is cloned and how.
This is still not efficient as it should be, because on every
HW change we drop all data structures and rebuild them from scratch
(which is not expensive because there aren't many of them, but
at least in the XRandR path it involves a few sync X calls)

https://bugzilla.gnome.org/show_bug.cgi?id=705670
Add the write side of the DBus protocol too

This is just in the documentation for now, to attract wider feedback
before we start looking at how to implement this for real.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
Extend the DBus XRandR protocol to expose cloning restriction

Turns out that even if two outputs say that they can be controlled
by a given CRTC, you can't configure them in the same CRTC unless
they are marked as "possible clones" one of the other.
This can further restrict the configuration options, so we need
to expose this limitation in the DBus API.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
DisplayConfig: add the write side of the API

Implement ApplyConfiguration in terms of XRandR calls.
Error checking is done before actually committing the configuration.

If mutter is using one of the other monitor config backends, an
error is reported and nothing happens.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
Reverse handling of XRandR events between Screen and MonitorManager

Now MonitorManager does its own handling of XRandR events, which
means we no longer handle ConfigureNotify on the root window.
MetaScreen reacts to MonitorManager::monitor-changed and updates
its internal state, including the new size.

This paves the way for doing display configuration using only
the dummy backend, which would allow testing wl_output interfaces.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
DisplayConfig: make the dummy backend writable

Add a number of dummy outputs and modes to the dummy backend,
and implement the writing bits.
The only visible effect is that you can change the screen size,
which resizes the output window.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
default plugin: add a random color background on each monitor

Instead of a full white background, make one with a random color.
This way the different "monitors" are visible and it's easier
to debug the DBus API.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
MonitorManager: fix handling of output transform

Read the current transform from XRandR, and expose the transforms
that are really supported on the bus.
The dummy backend now advertises all transforms, since it doesn't
actually apply them.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
MonitorManager: inherit directly from DisplayConfig instead of handling signals

This way we can handle properties too.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
MonitorManager: add support for DPMS levels

To the XRandR and dummy backend (and as usual the dummy backend
has no effect)

https://bugzilla.gnome.org/show_bug.cgi?id=705670
MonitorManager: add support for persistent monitor configurations

Add a new object, MetaMonitorConfig, that takes care of converting
between the logical configurations stored in monitors.xml and
the HW resources exposed by MonitorManager.
This commit includes loading and saving of configurations, but
still missing is the actual CRTC assignments and a default
configuration when none is found in the file.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
MonitorConfig: add CRTC assignment

Ripped off libgnome-desktop, trimming the parts that checked
that the configuration was plausible, as that should be done
in gnome-control-center before asking mutter for a change.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
MonitorConfig: add support for default configurations

Activate the presentation bit on new hotplugged monitors, while
making a fully extended setup when running for the first time.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
MonitorManager: store the presentation mode bit in XRandR

Use a private output property to store if the output is in
presentation mode or not, so that this information is not lost
after the configuration read back from the server.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
MonitorManager: further extend the dummy backend

The default configuration is extended, which is only possible
if there are as many CRTCs as outputs, so make sure that's true.

Also, add more and bigger modes, so that different sizes will
be chosen for the three outputs.
A nice side effect of this is that with a real 1920x1080 + 1600x900
layout, if you disable the VGA you get a stage that matches the
screen size, which triggers the legacy fullscreen path in the
outside mutter.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
MonitorManager: add support for backlight

GnomeRR needs that too.
The backlight is exported as a normalized 0-100 value, or -1 if not
supported. Clamping to HW limits is handled by the backend.
Changing backlight uses a different method call, to avoid recomputing
the full display configuration every time the user presses the
backlight keys.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
MonitorManager: ignore configuration changes that disable all outputs

If we compute a screen size of 0 in either direction, we crash
later on, as it is invalid for clutter, cogl and X.

https://bugzilla.gnome.org/show_bug.cgi?id=705670
MonitorManager: add gamma support

Add GetCrtcGamma() and SetCrtcGamma(), that wrap the similarly
named XRandR API. These are used by GnomeRR inside the color
plugin of the control center (and may go away if the color
plugin decides to do something different under wayland)

https://bugzilla.gnome.org/show_bug.cgi?id=705670