Rebuild textures if needed when moving a container

When moving a container to an output which has a different scale than
the previous, rebuild the title and marks textures at the new scale.

Fixes #1999.

include/sway/tree/container.h

@@ -98,6 +98,8 @@ struct sway_container {
 		// Passed the previous parent
 		struct wl_signal reparent;
 	} events;
+
+	struct wl_listener reparent;
 };
 
 struct sway_container *container_create(enum sway_container_type type);