mod reports: enable reporting for members, add dmail reporting.

* Add ability to report dmails.
* Enable reports for comments, forum posts, and dmails.
* Allow Members to send reports.
* Don't allow users to report the same thing twice.

app/models/comment.rb

@@ -129,7 +129,7 @@ class Comment < ApplicationRecord
   end
 
   def reportable_by?(user)
-    ModerationReport.enabled? && user.is_builder? && creator_id != user.id && !creator.is_moderator?
+    creator_id != user.id && !creator.is_moderator?
   end
 
   def voted_by?(user)