Remove support for django-reversion

[jrief]

django-reversion uses a JSON field to store a serialized version of the model fields. This in practice means that we would store our JSON payload inside another JSON field, which is kind of silly.

I therefore would suggest to rewrite the reversion functionality and add it to Cascade itself.

Side Note: The contributors of django-cms also want to remove support for reversion in their code base.

[rfleschenberg]

If django-cms removes reversion support, I see no reason why we should keep it. However, IMHO we should keep supporting reversion until we drop support for all django-cms releases that offer reversion support, unless keeping the reversion support is a big maintenance burden for us.

I am not so sure about adding versioning / undo support to cascade itself.

• Can this live in a separate app?
• What is django-cms's plan for the future? Switch to another solution, or drop reversion / undo support altogether?

[rfleschenberg]

czpython wrote on the django-cms mailing list:

The undo/redo functionality will come in our next 3.4.x release as its being developed separate from the core.

I suggest that we

• drop reversion support in all cascade releases that only support django-cms >= 3.4,
• wait until the django-cms undo/redo package is released before we start working on a possible undo/redo implementation of our own.