Provide http:// to parsec:// url redirection on backend to help url in mails

[touilleMan]

Sending mails with parsec:// urls doesn't seem to play well with various mail client for security purpose (see #1168)
A solution would be to provide a https://<url_to_backend>/link#type=<type>&token=<token> url, then make the corresponding loaded html page automatically rebuild and open the corresponding parsec:// url

This is kind of related to #676 given it requires to support http connections