make api wiki page retrieval consistent

test plan:
* use the wiki sidebar to create a link
to a new wiki page with a title containing
escapable characters (e.g. spaces)
* follow the link and create the page

* the link will look something like:
/courses/:course_id/pages/new%20page?titleize=0

* confirm that using that url in the api
(e.g. /api/v1/courses/:course_id/pages/new%20page)
retreives the page as well

closes #MBL-3057

Change-Id: I1aba32bef5558b545bf7024e22c3fea76643f231
Reviewed-on: https://gerrit.instructure.com/43145
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>