rename indexer.coll_druid_from_config for clarity
move assignment of url_fulltext from indexer to solr_doc_builder
clarifying context field
move collection record format logic to method that indexes the collection record
convert indexer.rb coll_formats_from_items to be an instance method instead of a class method
rename publix_xml_fields.rb coll_druids_from_rels_ext method (was collection_druids)