A search endpoint which spans types (e.g. Works, Authors, Subjects)

We have a single solr for all our different data types, so why not take advantage of it? This means a user could search for "j k rowling" and get a mix of authors/works(/editions? maybe) back, scored by solr by relevance, rendered differently. This is a little experimental and would be a decent amount of work, but not exceptionally challenging work since a lot of similar code already exists. Candidate for #603 hackathon!