Add field for country to campaign. Use that during synchronization

We need a way to grab country funds' associated country picture. Instead of using an ugly `LIKE` query, this explicitly stores the relevant country on the campaign object.

For now, it's unique (as only country funds use it), but we could remove that restriction if the country associated with memorial funds becomes relevant.

You'll notice some migrations to other fields; those are just description edits that weren't in `master`'s migrations.