mod_md: * Improved interface to mod_ssl for fallback handling. Backward compatible to previous mod_ssl patch, but fallbacks will not work. * Provide a temporary, self-signed certificate with a speaking command and domain name if we have no other cert for a Managed Domain, yet. Refs github issue #32 * Continue to provide expired or not-completely matching, existing certificate for a Managed Domain until the renewal was successful. This is helpful when one adds a DNS name to a MD, so the previous domains can be served while a new cert is requested. * All files necessary to run tests are not in the release package. * Making "http-01" the preferred challenge type again, as people "tls-sni-01" requires at least one working certificate vhost right now - which not everyone has. * moved part of the MD sanity checks from post_config to check_config phase, allowing for error detection in check-only runs.