If user name is available, take user to the Sign Up page

[ayan-b]

If a username is available, on clicking the icon it should take the user to the Sign Up page of the respective site.

[jayvdb]

Add a signup: key in websites.yml with the signup url, with url parameters as template variables, for a few sites.

Once a few are done, submit a PR.

Then we'll create new issues for adding signup support to the remainder of the websites, and other participants can help.