Iconfont icons are of no value to screenreader users; in our case,
they get alternative text. By adding 'aria-hidden="true"' to the
<span> holding the iconfont icon, we avoid the screenreader trying
to announce the iconfont icon.
This includes only the icons actually used or intended to be used
in the backend. Please note that unfortunately, some class names
have changed. Also some icons have been exchanged.
