Don't call a lifecycle hook twice with the same state.

[garyd203]

This allows users to listen for multiple specific change events and handle them all in a single function.

I tried to follow the existing style for testing. Let me know if you would prefer a different approach, squashed migrations, etc.

[garyd203]

Thanks @Faisal-Manzer , I have rebased my PR and updated the changes to suit the current codebase. Tests pass on my local machine.

Cheers,
gary

[Maushundb]

+1 on merging this - looks like when_any fires the hook once per field changed, even if .save() was only called once on the model. @rsinger86