Update things to work with newer versions of Django

[evz]

Greetings! I'm trying to work on a few election related things up in my new home county just north of Milwaukee. I was hoping to incorporate some of the opencivicdata models into the project and hit a bit of a roadblock since it seems that it's been a while since anyone has updated the Django version here. I'm not entirely sure where this project left off in terms of Django versions but it would seem that anything newer than perhaps Django 3.0 won't work because of some of the ways in which they've modified how models and index creation work. Specifically:

• JSONField is now supported for all DB backends This means that the imports are different there, basically
• index_together is deprecated in favor of indexes Rather than passing a list of fields you'd like to create and index for, you pass a list of models.Index objects that include the fields you'd like to index.

I updated the models and migrations to reflect these changes and tested it out against the latest Django release. I'm not sure how necessary it might be to support versions between 3.0 and 4.2. If that's something that we'll want to do here, I can break these changes out into two different PRs so that it's simpler to cut two different versions.

Anyways, I really hope someone is out there listening still! I notice that @fgregg has been in here in the past year or so which gives me hope!

[fgregg]

hi eric! the james mckinney just fixed the jsonfield thing (like this week). can you rebase off of that?

[evz]

Ha! I just did.

[evz]

Sorry about the noise here. This is one of those things I thought was gonna be simple.

[fgregg]

no problem. looks like you have some linting issues left?