add loading class for mdo to style on customizer
add loading class for mdo to style on customizer

BS3 commit dec00eeeafaa1272b8fc3754b8d134e8d358a6ed

2947721120/googlebt4,aaroncnhk/todc-bootstrap,mozillo/todc-bootstrap,2947721120/todc-bootstrap,todc/todc-bootstrap,todc/todc-bootstrap,todc/todc-bootstrap,ztx1491/todc-bootstrap,up2vs/todc-bootstrap