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.
They could, except that module was designed to be included in a model.  I create this module so that these methods could be shared between an AF model and a solr document, Sufia::SolrDocumentBehavior.  There are other things in Hydra::AccessControls::Visibility that, if included in SolrDocumentBehavior, would cause errors if called.  For example, the bits about datastreams.

I suppose on option would be to put the module somewhere else in hydra-access-controls.

@jcoyne thoughts?