api(align) save align in style and handle x/y according to it

examples/widgets/chart/lv_example_chart_2.c

@@ -62,7 +62,7 @@ void lv_example_chart_2(void)
     /*Create a chart1*/
     chart1 = lv_chart_create(lv_scr_act());
     lv_obj_set_size(chart1, 200, 150);
-    lv_obj_align(chart1, NULL, LV_ALIGN_CENTER, 0, 0);
+    lv_obj_center(chart1);
     lv_chart_set_type(chart1, LV_CHART_TYPE_LINE);   /*Show lines and points too*/
 
     lv_obj_add_event_cb(chart1, event_cb, NULL);