Fix Font Awesome markup and CSS

Here is the patch with both CSS and markup fixes.
AXE has no issues with that: https://jsfiddle.net/s23w8q4j/

Fixing tests...

This patch #9 worked for me! Thank you so much!

Is `sr-only` a native Drupal CSS class? I don't know so asking. I think traditionally `visually-hidden` may be the more appropriate class to use here. So I'd take the patch in the related issue over this one.

Hello @Baysaa,

sr-only is a fontawesome-specific class, added since version 4.6.0 (commit)
I'm not a maintainer but I'm not against changing it to "visually-hidden" which would make it independent from any FA version.
Feel free to post a patch.

Path #9 worked for me as well. Thanks!

Thanks, could this please be turned into a MR for further review and merge?

Hi @Anybody, sure, done.

@herved if the icon's using FA then it makes sense that sr-only should also work, thanks!

Think visually hidden would be better as even though we have font awesome icons the library might not be present (so the checkbox setting is unchecked) so not sure sr-only would cover all cases.