Move ModelDecorator to a new file; Remove duplicate PaginatingDecorator

Move `ModelDecorator` to a new file now that we know it works and that
we're going to use it. I had previously put these two classes in the
same file as `ReferentialDecorator` because I wanted to test that it
worked before making the code correct.

Also remove the `PaginatingDecorator` because apparently we already have
one, which I didn't realise. Use the existing one instead.

Refs #3479

2 files changed, 3 insertions, 17 deletions

diff --git a/app/decorators/model_decorator.rb b/app/decorators/model_decorator.rb
new file mode 100644
index 000000000..dee014cc3
--- /dev/null
+++ b/app/decorators/model_decorator.rb
@@ -0,0 +1,3 @@
+class ModelDecorator < PaginatingDecorator
+  delegate :model
+end
diff --git a/app/decorators/referential_decorator.rb b/app/decorators/referential_decorator.rb
index 45a4b38d1..1c2347529 100644
--- a/app/decorators/referential_decorator.rb
+++ b/app/decorators/referential_decorator.rb
@@ -1,20 +1,3 @@
-# Delegates 'will_paginate' methods
-class PaginatingDecorator < Draper::CollectionDecorator
-  delegate(
-    :current_page,
-    :per_page,
-    :offset,
-    :total_entries,
-    :total_pages
-  )
-end
-
-
-class ModelDecorator < PaginatingDecorator
-  delegate :model
-end
-
-
 class ReferentialDecorator < Draper::Decorator
   delegate_all