Manually translate legacy to new property names.

When starting the S3Mock directly from Java with an
"application.properties" in the  classpath, the S3Mock's bundled
"application.properties" is not found anymore, so we can't do property
translation there.

Implementing a poor man's property translation that directly interferes
with Spring's "Externalized Properties" precedence order here.
Need to deprecate direct usage and remove this ASAP.

Fixes #434

Probably breaks other integrations, we'll see...