Fix backward compatibility with the ACL enricher

In 6.0, the node listing the ACES was named ace, see ACLContentEnricher
Since 7.10 and NXP-18038, the node is named aces, see ACLJsonEnricher which is better because it represents an array but breaks the backward compatibility.

We need to find a way to provide backward compat, maybe by adding a ace node when a system property indicates that a 6.0 compat is needed.

Add a global flag to enable/disable the 6.0 compatibility nuxeo.lts2014.compatibility.enabled