add ids to export

[shapiromatron]

Added HERO, PubMed, and DOI values to risk of bias, animal, epi, epi meta, and in vitro exports.

[munnsmunns]

@shapiromatron Let me know what you think of these changes

[shapiromatron]

I think it'd be better if we could keep the serializers as is, and then just insert the columns after they export had been created. There's a method here that I think gives all the data we need, on a reference queryset (which could be the ids from the study queryset:

models.Reference.objects.identifiers_dataframe(qs)

[shapiromatron]

Awesome job Matt. I had grand ideas to refactor what you did to make the study evaluations and invitro to use the same approach as the other exports, but once I started, I realized it would take a lot more work to complete. I would have done it exactly as you did.

The only change I made was moving the identifier data frame creation from the common app to the Study app, since its more a property of studies.

[munnsmunns]

Thanks Andy! The changes look good