deprecate hide_from_students on wiki pages

hide_from_students is being deprecated in lieu of the workflow states
'active' (published) and 'unpublished'

test plan: (draft state and legacy)
  special attention should be given to areas related to hiding wiki
  pages from students (legacy: hide from students checkbox;
  draft state: published/unpublished items)

  items that are hidden from students or unpublished should show for
  teachers, but should not show for students

 - areas to test:
   - pages api and ui (regression)
     - validate hide_from_students and published values in all api calls
   - course migrations (specifically course copy)
   - wiki sidebar in other parts of canvas

fixes CNVS-10354, CNVS-10366

Change-Id: I70f4d8c07c2be4150163279f0673377bad6e9c48
Reviewed-on: https://gerrit.instructure.com/28375
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>