Redirect from admin editor to frontend post view

closes #2628
- added /view/ route to the editor. if /view/ is appended to
  the url of a post being edited a redirect to the frontend
  will occur
- updated controller to check for /view/ and built the
  correct url for the post
- added test for the new route
Merge pull request #2670 from jaswilli/issue-2628

Redirect from admin editor to frontend post view