clients/window: Add functions to set/retrieve app_id

Adds appid for all clients using the toolkit, flower, fullscreen, image,
resizor, scaler, smoke, stacking, subsurfaces, terminal,
touch-calibrator, transformed, etc.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
diff --git a/clients/fullscreen.c b/clients/fullscreen.c
index 5dfd3c5..ccedfbc 100644
--- a/clients/fullscreen.c
+++ b/clients/fullscreen.c
@@ -550,6 +550,7 @@
 		window_add_widget(fullscreen.window, &fullscreen);
 
 	window_set_title(fullscreen.window, "Fullscreen");
+	window_set_appid(fullscreen.window, "org.freedesktop.weston.fullscreen");
 
 	widget_set_transparent(fullscreen.widget, 0);