comments: add scores, rework comment menu.

* Add comment scores.
* Rework voting buttons so that you can click the upvote/downvote
  buttons to toggle votes.
* Hide the edit, delete, undelete, and report buttons behind a popup menu.
* Show the upvote/downvote/reply buttons to logged out users. Redirect
  them to the login page instead.

app/policies/comment_policy.rb

@@ -20,12 +20,7 @@ class CommentPolicy < ApplicationPolicy
   end
 
   def reply?
-    create? && !record.is_deleted?
-  end
-
-  def vote?
-    # XXX should use CommentVotePolicy
-    unbanned? && !record.is_deleted?
+    !record.is_deleted?
   end
 
   def permitted_attributes_for_create