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>