Support file uploads

This allows submissions to store file uploads

app/jobs/submission_append_job.rb

@@ -0,0 +1,8 @@
+class SubmissionAppendJob < ApplicationJob
+  queue_as :default
+
+  def perform(submission_id)
+    submission = Submission.find(submission_id)
+    submission.append_to_spreadsheet
+  end
+end