Add Instagram and maybe Giphy to social media links

Among other places, the "course about page" shows social media links. Currently it only links to Facebook and Twitter, but we should see if we can expand it to include Instagram and our Giphy page as well, so people can find our social media more easily.

Please don't use any APIs or sources from Giphy or Instagram to include this: we definitely don't want Totem to do a call to Instagram or Giphy when people load the course about page.