deposit: duplicate validator with prod inspirehep

One issue, but it's not a problem of the validator itself, rather our import logic: on import, even if there are some validation errors, the id is imported.

depends on: 
https://github.com/inspirehep/inspire-next/pull/105
https://github.com/inveniosoftware/invenio/pull/2433
You have already ```from .validators.simple_fields``` - add that import there. And keep the Invenio imports at the end.