Add versioning support to NegotiationCards and TestSpec

[sebastian-echeverria]

Add a way to support versions for NegotiationCards and TestSpecs. This will have to be implemented in each backend store as well. The idea is to keep versions of each every time they are save()d into a store, instead of overrwriting the current one.

[sei-aderr]

I think we may not want to have a new version for every time the user saved the negotiation card. On large changes it would make sense but the amount of cards could get bloated if they need to make small changes or as they work initially and want to save their work. Potentially an option to save as a new version when saving in the frontend, or something similar. Can discuss more