Patch for review - Reset dirty attributes #1954

Hi,

I've attached an updated patch to lighthouse ticket 1954 which implements the resetting of attributes on a model to their original values. The ticket was stale at the time I updated it and remained stale afterwards and so I'm not sure how many people would have seen it.

I'd appreciate it if someone could 'unstale' the ticket if that makes sense and appreciate it even more if others could review the patch.

Paul