Make a QWindow-based compositor and rename the original desktop compositor

QtQuick compositors don't work very well, so we need to use a QWindow-
based compositor until QtQuick support works.
Refactor desktop compositor

Refactor code a little bit and add support for resizing.
Pass initial geometry when creating a compositor

Always pass an initial geometry.
Add server-side Wayland protocol implementation

This will need more work.
Disable compositors build make the shell working with Weston

QtCompositor and kms support are immature and Qt 5.1 is focused on
getting the QPA plugin done, so compositor improvements are scheduled
for Qt 5.2, in fact the QtCompositor library is not built by default
because it's an experimental API.

This leaves me no choice but port the desktop shell to Weston.

Compositors are excluded from the build.

Issue: #23
Turn background into a QtQuick window

Background is now totally QML, makes it easier to work with.

Issue: #23
Don't handle wl_output

Let QPA plugin do it for us.

Issue: #23
Turn launcher into a QtQuick window

Launcher is now totally QML, this makes it easier to work with.

Issue: #23
Use Q_GLOBAL_STATIC

It's way better to make singletons.

Issue: #23
Set initial geometry

VCompositor API slightly changed, now an initial geometry is passed to
the compositor when it creates the output window.
QWindow-based compositor is now called "classic"

Main goal of this compositor is to be a simple desktop compositor
without too much animations and effects.
One day we might think about writing a specific shell.

We keep this compositor temporarily disabled until it has been
ported to the new QtCompositor API.
Initial desktop_shell interface implementation

Start writing code to implement Weston's desktop_shell interface.

Issue: #23
QML-based desktop shell becomes "desktop" again.

Rename the plugin to "desktop".
Fix shell surfaces creation

Move shell surfaces creation to WaylandIntegration and don't set user
data to the object that creates the window otherwise QPA plugin will
crash because it expect a QWindow. The wayland QPA plugin already sets
the user data to QWindow, though.
We also don't want to listen to Wayland events anymore since outputs
are already handled by QPA.
Launcher size depends on screen size

During startup Launcher size is set according to the screen size, we
also listen for screen geometry changes to change the launcher size.

Issue: #23
Use transparent color for the Launcher window

Avoid drawing a background by setting the color to "transparent".

Issue: #23
Special window management for shell windows

Shell windows are always on top and don't need a window chrome.

Issue: #23
Make updateScreenGeometry() public

Let screen geometry be changed from other places as well.

Issue: #23
Detect screen geometry changes for the background

Change window geometry as screen geometry changes.

Issue: #23
Fix typo

Change "Background" to "Launcher".