Add index authors solr document mixin (logic ported from old codebase).
Pass options through SolrDocument#collection_members to CollectionMembers class.
Add collection member enumration helper method.
Add file collection members partial.
Add index and show partials for file collection objects.
Merge pull request #179 from sul-dlss/file-coll

Create File Collection views
Add 'In collection' access panel to metadata panels section.

Add druid mixin to extract the druid reliably from any purls in index URLs.