Application panel "more applications" dropdown display is wrong on Chrome

This is a regression introduced in:

https://github.com/xwiki/xwiki-platform/commit/7f8e72a8db9496561741f1413ea3452b2ba48b7d

The `text-align` CSS property is not interpreted exactly the same by Chrome and Firefox, our UC works properly on FF but not Chrome. We need to find an alternative to center the icon.