Feature/uuid versions

The django migration that drops and re-adds the `version` field on the `Indicator` model is because migrations failed to pick up the type change for the `to_field` on the foreign key.
For now -- I think version has a slightly different meaning because really it is going to be used to distinguish between indicators for different scenarios eventually, so latest version isn't really going to be a thing at some point. We're a bit off from scenarios though.