Fixed: Forgot to remove corpora from facets
New: Models for new fields

Based off of the model for corpora
Added: M2M relationships in piece/mvt models + serializers

This is for indexing and serializing the new fields
Added: New fields to admin, solr_indexing in piece/mvt models

Fields should now be indexed upon piece/mvt model's saving, and should be serializable in the admin interface
Added: New Fields in Solr Schema

With copy fields for both general and advanced searching.