add checkbox for include in repository

lets the teacher decide if the students
turn it in paper gets submitted to the
repository or not

closes PS-1863

test plan:
  1. enable turnitin
  2. create an assignment
     with turnitin enabled
  3. go to Advanced Turnitin Settings
  4. validate new checkbox for include
     in repository is there
  5. validate you can check it and
     uncheck it and save the assignment
     and the setting stays for that assignment
  6. uncheck it as a teacher and save the assignment
  7. submit the assignment as a student with a file
     upload essay
  8. Originality Report should come back as a new
     submission
  9. revise the essay file upload and resubmit
     the Originality Report should come back as
     a new submission

old behavior:
  1. first submission Originality Report was fine
     once revised and submitted again the Originality
     Report was coming back as plagiarized because
     it was comparing the revised essay against
     the first submission. this is undesirable

Change-Id: I85770425e53c3b9bc50a2591125ce45f253b9cf2
Reviewed-on: https://gerrit.instructure.com/38592
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>
Product-Review: Jake Sorce <jake@instructure.com>