Add idle inhibitor support

With this, some apps (e.g. mpv) can block the idle tracker from
kicking in. This way, the screen won't blank (or whatever you
configured) when the application doesn't want it to.

meson.build

@@ -56,6 +56,7 @@ conf_data.set10('CAGE_HAS_XWAYLAND', get_option('xwayland'))
 
 cage_sources = [
   'cage.c',
+  'idle_inhibit_v1.c',
   'output.c',
   'seat.c',
   'view.c',
@@ -66,6 +67,7 @@ cage_headers = [
   configure_file(input: 'config.h.in',
 		 output: 'config.h',
 		 configuration: conf_data),
+  'idle_inhibit_v1.h',
   'output.h',
   'seat.h',
   'server.h',