No need to include all ActionView::Helpers in Topic (PR #1139)

No need to include all ActionView::Helpers in Topic, we only need the sanitize helper.

This also fixes a bug in Rails 4 where image_url gets accidentally overridden.

GitHub

You’ve signed the CLA, stephankaag. Thank you! This pull request is ready for review.

true, that is a good point :+1: