43810817 configure enums with import

This is a pretty hack-ridden solution to the problem of imported records with invalid controlled values raising errors. In order to do this as non disruptively as possible, everything's being done via the 'rescue' method for now. (rescue validation errors, bypass them if the error arises from a dynamic enum field, modify enumerations with the illegal values reported by the validator).

I've only tested this against a small data sample, so it's likely incomplete. However, the AT Tracer MARC record will now import without having its extent_types remapped first.

https://github.com/hudmol/archivesspace/blob/master/migrations/examples/marc/at-tracer-marc-1.xml

We'll need to do something about the frontend not having translations for enums that get populated this way.