docs: update the "SSL Strong Encryption" how-to

The how-to was a little behind the times. Update to modern ciphersuite
selections, and teach the reader more about *why* certain selections and
settings are chosen. Try to future-proof a little bit by including the
"last-reviewed" date and pointing to Mozilla's recommendation tool.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1757280 13f79535-47bb-0310-9956-ffa450edef68