refactored view visibility

- replace visibilty mask integers with an enum
- set output's visibilty mask on creation
- added update_visibility to manually update a containers visibility (e.g. when it moved to an invisible workspace)

sway/handlers.c

@@ -90,6 +90,9 @@ swayc_t *container_under_pointer(void) {
 static bool handle_output_created(wlc_handle output) {
 	swayc_t *op = new_output(output);
 
+	// Visibilty mask to be able to make view invisible
+	wlc_output_set_mask(output, VISIBLE);
+
 	if (!op) {
 		return false;
 	}