kiosk-shell: Introduce kiosk/fullscreen shell for desktop apps

kiosk-shell is fullscreen shell for apps that use the xdg-shell
protocol. The goal is to make life easier for people shipping embedded
devices with simple fullscreen shell requirements, and reduce the
proliferation of desktop-shell hacks.

Top level surfaces are made fullscreen, whereas dialogs are placed on
top in the center of the output and retain their natural sizes. Dialogs
can be moved and (un)maximized, but resizing is currently not supported.

An app can be directed to a particular output by populating the
"app-ids" field with the app's XDG app id, in the relevant
"[output]" section in the weston config file.

Fixes: #277

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>

doc/sphinx/index.rst

@@ -7,6 +7,7 @@ Welcome to Weston documentation!
 
    toc/libweston.rst
    toc/test-suite.rst
+   toc/kiosk-shell.rst
 
 Weston
 ------

doc/sphinx/toc/kiosk-shell.rst

@@ -0,0 +1,17 @@
+Weston kiosk-shell
+==================
+
+Weston's kiosk-shell is a simple shell targeted at single-app/kiosk use cases.
+It makes all top-level application windows fullscreen, and supports defining
+which applications to place on particular outputs. This is achieved with the
+``app-ids=`` field in the corresponding output section in weston.ini. For
+example:
+
+.. code-block:: ini
+
+    [output]
+    name=screen0
+    app-ids=org.domain.app1,com.domain.app2
+
+To run weston with kiosk-shell set ``shell=kiosk-shell.so`` in weston.ini, or
+use the ``--shell=kiosk-shell.so`` command-line option.

doc/sphinx/toc/meson.build

@@ -1,5 +1,6 @@
 # you need to add here any files you add to the toc directory as well
 files = [
+	'kiosk-shell.rst',
 	'libweston.rst',
 	'test-suite.rst',
 	'test-suite-api.rst',