Do not add the $site_address in generated tokens

Let the web client add the protocol and site address.

The problem is that the protocol part of the URL is "http:" even for
sites in "https:"
My problem was that the Apache rewrite rule to redirect a http: page to
the https: equivalent corrupted the URL.

See bug #240 "Guest token does not work correctly for folders containing
accents" https://github.com/thibaud-rohmer/PhotoShow/issues/240
Merge pull request #4 from LudovicRousseau/guest-token

Do not add the $site_address in generated tokens