[SAC] Libre avatar support added to the experimental Gogs deploy

I've upgraded the Gogs experimental service to a version which
supports federated avatars. This means you can configure your
domain to advertise your own means to provide avatars for
email under that domain.

More info about the libre avatar project: https://libravatar.org

If DNS doesn't specify any source for domain avatars, the clients
will be instructed to ask for an avatar to the libravatar.org CDN service
(only the hash of the email is sent to the client and the CDN service)
which makes it convenient to manage avatars to those who do not have
control over their email domain or do not want to manage a new service
in house.

Finally, if an entry is not present in the libravatar.org CDN, the
service will redirect the browser to gravatar.com, which is the
currently affirmed service for centralized avatars (used by github
and wordpress, for example). So those of you (many) who already
have an account on gravatar.com will still have their avatar pop up.

Take a look:

Those who want to get back control over their avatars can find out
how here: https://wiki.libravatar.org/running_your_own/