Bug 40458: Implement .tor.onion aliases

We have enabled HTTPS-Only mode, therefore we do not need
HTTPS-Everywhere anymore.
However, we want to keep supporting .tor.onion aliases (especially for
securedrop).
Therefore, in this patch we implemented the parsing of HTTPS-Everywhere
rulesets, and the redirect of .tor.onion domains.
Actually, Tor Browser believes they are actual domains. We change them
on the fly on the SOCKS proxy requests to resolve the domain, and on
the code that verifies HTTPS certificates.