Moving FileSet and NewspaperIssue definition to specs

Before this commit, these files were something that all applications
would load into their production code.  Ideally, we don't want to do
that for the two reasons:

- First, not everyone wants a NewspaperIssue model in their application

- Second the file_set, as implemented, directly inherits from
  `ActiveFedora::Base`.  If a downstream FileSet were to not inherit
  from `ActiveFedora:Base` we would have a mismatch error.

With this commit, we're saying that the IIIF print gem will require a
FileSet that conforms to the PCDM expectations.  But we won't dictate
its implementation details in the downstream application.  We instead
dictate those implementation details in the test application.

Also we will not force downstream Hyrax implementations to include a
NewspaperIssue model.

Related to:

- #101

spec/support/iiif_print_models.rb

@@ -1,4 +1,28 @@
 # frozen_string_literal: true
+###################################################################################################
+#
+# The purpose of this file is to define the models we'll use in our spec application.  Some of these
+# models are echoes of what downstream apps will define (e.g. FileSet).  Other are for internal
+# modeling purposes only.
+#
+####################################################################################################
+
+##
+# iiif_print requires a file set model that is compatible with Hyrax assumptions.  We do not want to
+# add this to app/models because those are loaded in the downstream application; which can create
+class FileSet < ActiveFedora::Base
+  include ::Hyrax::FileSetBehavior
+end
+
+# Newspaper Issue
+class NewspaperIssue < ActiveFedora::Base
+  # WorkBehavior mixes in minimal ::Hyrax::CoreMetadata fields of
+  # depositor, title, date_uploaded, and date_modified.
+  # https://samvera.github.io/customize-metadata-model.html#core-metadata
+  include ::Hyrax::WorkBehavior
+  # BasicMetadata must be included last
+  include ::Hyrax::BasicMetadata
+end
 
 # TODO: merge this in with whatever is needed from misc_shared.rb
 class WorkWithIiifPrintConfig < ActiveFedora::Base