Use order-agnostic comparison for JSON

[fyrts]

The current implementation for dealing with MySQL reordering of JSON keys assumes that MySQL sorts the keys alphabetically, which isn't always the case.

From the MySQL documentation:

To make lookups more efficient, it also sorts the keys of a JSON object. You should be aware that the result of this ordering is subject to change and not guaranteed to be consistent across releases.

I've changed the preSave method to ignore any differences in order by comparing sorted versions of the original and changed JSON data.