Feature/collection facet

@NYULibraries/hydra In this PR there are two major changes:

1. A collection facet is mapped from various fields (namely type and publisher) via a `collection_map.yml` and sent to solr via the `to_solr` method in the Nyucore model
2. While I was in the Nyucore model i removed the multiples lines of `has_attributes` into two lines as a PoC for going forward in reworking the Nyucore class/having all Ichabod fields in one place in the stack.

This was the only implementation I could think of for getting an additional field in solr that is not in the source data and needs to be mapped to text that doesn't exist anywhere outside the application context. The usage of `to_solr` for pre-solr processing is standard in blacklight and hydra. I'm open to alternative suggestions of course.

I also refactored the `:nyucore` factory a bit since it was getting messy and made the appropriate spec and cuke changes to keep tests passing.