[Feature] Add Tor links to main page (and child pages)

[Atrate]

For now, when visiting Riseup via the Tor hidden service, when someone clicks on any link that would redirect to a subdomain (e.g. mail.riseup.net), they will be redirected to the clearnet version of the site.

This could be solved by e.g. putting small, superscript Tor links next to the existing hyperlinks.

[just1602]

For now there's gonna be a link to the file with all the onion addresses in the footer of every page, but the services links (email, list, etc) won't be changed in the pages since it would required two deployment of the website (this oone and another one for the hidden service) or JavaScript which is probably gonna be disabled in Tor Browser anyway.

I'll let the issue open in case we come up with a better solution in the future.