Display links to author mastodon/twitter

[rauhul]

The authors yaml file currently has a twitter field that doesn't appear in the swift.org UI anywhere (as far as I can tell). It would be nice to display this information as a clickable icon and include support for mastodon profiles

[dempseyatgithub]

After discussion, the website workgroup decided that instead of adding links to multiple profiles per author across multiple services, the site will use only GitHub profile links for author profiles.

A more detailed explanation of the decision is in the closed PR:
#481 (comment)