* Let the user see their own username when viewing their own deleted comments.
* Don't hide the creator_id field from the comment creator in the API.
* Hide the score, do_not_bump_post, and is_sticky fields for deleted
comments in the HTML and in the API, unless the user is a moderator.
* Hide the "..." popup menu on deleted comments, unless the user is a moderator.
This is so that when a user looks at their own comment history, their
name isn't hidden from them on their own deleted comments. This may confuse
users however into thinking their name is still visible to other users.
Make it so that when a user removes their own vote, the vote is soft
deleted (the is_deleted flag is set) instead of hard deleted.
Changes:
* Add is_deleted flag to comment votes.
* Relax uniqueness constraint so you can have multiple deleted votes on
the same comment. You can still only have one active vote on the comment.
* Add `soft_delete` method to Deletable concern.
Let users see when a post has deleted comments. Show normal users a
'[deleted]' placeholder when a comment is deleted. Show the full comment
to moderators.
Also fix it so that the comment creator can't edit or undelete deleted
comments, and users can't vote on or report deleted comments.
Finally, hide the creator_id, updater_id, and body of deleted comments
in the API.
Previously thresholded comments were hidden completely. You had to click
the "Show X hidden comments" button to unhide all hidden comments in a
thread. Now it works like this:
* When a comment is below your threshold, the comment text is hidden and
replaced by a `[hidden]` link, which you can click to unhide the comment.
* When a comment is at half your threshold (for example, your threshold
is -8 but the comment is at -4), then the comment is greyed out.
This means that comments aren't completely hidden, they're just
collapsed, so you can see the commenter and the score without unhiding
the comment. It also means you don't have to scroll back up to unhide a
comment, and threads aren't disrupted by comments being secretly
hidden (which is confusing when people are replying to hidden comments,
which forces you to go back up and unhide to find).
