Convert CarrierResource and RegionResource to DRF (bug 910616, bug 940352)

https://bugzilla.mozilla.org/show_bug.cgi?id=910616
https://bugzilla.mozilla.org/show_bug.cgi?id=940352

Note: we have *another* `RegionResource` in `mk.regions.api` that I left alone, it's for App serialization so I think it should be covered by the `AppResource` conversion. It doesn't serialize the same way.