Prepare for email templates

This includes moving res/templates to res/webpages, and the creation of
res/emails. The code which loads the templates has been moved to
nodeatlas.go, and it uses the globs "<*fRes>/templates/*.html" and
"<*fRes>/emails/*.txt".
Add email-sending support

Verification is not yet implemented, but emails can be sent
unauthenticated. The fields SMTP and Hostname have been added to the
configuration. See config.go for details.

Ref #8
Fix inconsistencies with Conf.Prefix
Add verification by email

If SMTP is implicitly enabled (Conf.SMTP != nil), then an email is sent
via configured SMTP values to the email address provided when someone
registers a node. This contains a pseudorandom 64-bit integer (see #14),
which can be submitted to /api/verify in order to move the new node from
the nodes_verify_queue to the nodes table.

Close #8