update twitter icon/url on community page
- change twitter.com URL to x.com
- update fontawesome files to latest version that contains fa-x-twitter
- add aria-hidden="true" to Mastodon icon
- remove leftover font-awesome.min.css which was not used
Note: I've set the header to "X.com" instead of just X or it looks a bit weird to have X X. Removing the text looks good (leaving just the icon) but then we end up with an empty h2 element and no title for this section for screen readers.