should admin integration ignore fields with editable=False by default ?

[olivierdalang]

Hi ! Thanks for this awesome package !!

I'm testing it out with a model where I have a fairly large json field to attach some technical information to my instances. This field is declared with editable=False, as it's not meant to be edited through forms. However, django-reversion still serializes it, making the revisions table huge.

IMO, with the default admin integration, it would make sense to exclude fields with editable=False. For specific cases, it's better to manually register the models anyways.

Since this wouldn't be backwards compatible, maybe this behaviour could be behind a setting ?

Let me know what you think. I may be able to contribute this feature if you think it's a good addition.