Hiding comments workflow

* Reorganises the flow_page.rb so dialog easier to find and reuse
* Adds browser tests to show expected behaviour
* Apply styling for moderated posts to moderated comments
* Correct the moderatePost callback to modify the correct element so that
the moderation class is added or removed where appropriate.

Change-Id: If2fe4653734c5c751bb271dd7ad25b20a295bbe1
Merge "Hiding comments workflow" into frontend-rewrite