Update output manager on layout change

The output manager config was not properly updated if the position
of the output got changed.

include/sway/server.h

@@ -34,6 +34,7 @@ struct sway_server {
 	struct sway_input_manager *input;
 
 	struct wl_listener new_output;
+	struct wl_listener output_layout_change;
 
 	struct wlr_idle *idle;
 	struct sway_idle_inhibit_manager_v1 *idle_inhibit_manager_v1;