Integrate comment moderation prototypes

Misc:
* Flag-related stuff is not yet implemented
* rename `comments_review` function as `comment_moderation` to match language used elsewhere
* utility function `detail_link` now supports linking to users and to `MapFeature` subclasses like `Plot`
* Fix initialization of photo review page
Merge pull request #1593 from RickMohr/integrate-comment-moderation

Integrate comment moderation prototypes