add non_digital_submission to assignment

refs CNVS-15324

no test plan

Change-Id: Ia60a27829ad86e13e1540a0e32c8e2d5bbbd3b0a
Reviewed-on: https://gerrit.instructure.com/46595
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Steven Burnett <sburnett@instructure.com>
QA-Review: Mike Nomitch <mnomitch@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>

app/models/assignment.rb

@@ -1734,6 +1734,10 @@ class Assignment < ActiveRecord::Base
     submission_types == 'on_paper' || submission_types == 'external_tool'
   end
 
+  def non_digital_submission?
+    ["on_paper","none","not_graded",""].include?(submission_types.strip)
+  end
+
   def allow_google_docs_submission?
     self.submission_types &&
       self.submission_types.match(/online_upload/) &&