In some cases, field classes may be renamed or moved to different modules. django-evolution had some one-off logic to handle this for when django itself moved all the fields from `django.db.models.fields` to `django.db.models`, but there was nothing available to consumers of the library to do the same. We recently ran into a problem where we decided to remove a dependency on a third-party field, replacing it with a compatible home-grown implementation. This worked fine, except django-evolution would fail to load the signature because the old module didn't exist. This change adds a new mapping to the django-evolution configuration, `RENAMED_FIELD_TYPES`, which allows a project to define their own renames. Testing Done: - Used this in conjunction with code that set `DJANGO_EVOLUTION['RENAMED_FIELD_TYPES']` to a mapping from our old third-party library to our new implementation, and saw that django-evolution management commands and `Evolver` calls worked correctly. - Ran unit tests.