MODE-2309 Corrected reading and writing JSON files when escaped characters are used ('master' branch)

This fixes the backup and restore issue. Note that ModeShape uses BSON when storing nodes in Infinispan, so this should not affect persistent storage in a cache store. ModeShape uses JSON for the file connector (extra properties) and for the REST service; neither of these should be impacted negatively by this change, though like the backup and restore this change should fix any as-of-yet unseen issues related to escaped characters.

Note that it is not possible to just update the Restore functionality, so with this change new backups will have to be created. This change does need to be applied to the 3.x branch as well.
JSON requires that all non-printable characters also be escaped as unicode. I'll add a comment, tho.