Don't hardcode social media links in first-run page

[greiner]

Background

The links to our social media pages on the first-run page are currently hardcoded which means that we cannot easily update them in case they change. Usually, we use Utils.getDocLink() to create links that redirect to external pages. In #2734 we added such redirects for all of our social media pages so we should make use of those in the first-run page.

What to change

Use Utils.getDocLink() to dynamically create links to all of our social media pages and remove the existing hardcoded ones from firstRun.html.

[agiammarchi]

I believe we are already using getDocLink within the click handler:

  function onSocialLinkClick(event)
  {
    if (window.matchMedia("(max-width: 970px)").matches)
      return;

    event.preventDefault();

    getDocLink(event.target.id, (link) =>
    {
      openSharePopup(link);
    });
  }

Should the link pre-set befre the click or can we just close this ticket?

[greiner]

This is about the fallback links which are used when Adblock Plus is configured to block social media scripts. Those links are hardcoded in firstRun.html.

We're going to rewrite the first-run page in #5894 so we can tackle it as part of that one to ensure that we're not making the same mistake again.