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.
The impetus for this PR was to put methods like `registered?` and `public?` in a module that's sharable between an AF model and a solr document.  Since the solr document isn't going to be able set any of the permissions values, maybe setters can be in Permissions and getters in Visibility.

There's also the duplication of [public?](https://github.com/projecthydra/sufia/blob/master/sufia-models/app/models/concerns/sufia/generic_file/permissions.rb#L37) in Sufia::GenericFile::Permissions as well.

@jcoyne Any suggestions here?  We can talk about it at today's standup.