shell: use desktop-shell ini file for screensaver path

Read the same configuration file in the shell plugin (desktop-shell) as
the desktop-shell client does.

Add a new section "screensaver", where "path" defines the path of the
idle animation client to be executed. Not defining "path" disables the
animation.

Idle animations are not in use by default. It must be configured in
wayland-desktop-shell.ini or launched manually.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/wayland-desktop-shell.ini b/wayland-desktop-shell.ini
index 3a86935..d438a85 100644
--- a/wayland-desktop-shell.ini
+++ b/wayland-desktop-shell.ini
@@ -18,3 +18,7 @@
 [launcher]
 icon=/usr/share/icons/gnome/24x24/apps/arts.png
 path=./clients/flower
+
+[screensaver]
+#path=./clients/wscreensaver
+