Visibility status in show and list views

Creates a `Sufia::GenericFile::Visibility` module, used either in the model or its solr document, which define methods used to display information about a file's visibility.  Helper methods take care of displaying labels with the pertinent information.
Rspec takes care of that `expect(subject.registered?).to be true` is equivalent to `expect(subject).to be_registered`.  (it can also convert has to have, and handle parameters)