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).
This refactors Pundit policies to only rely on the current user, not on
the current user and the current HTTP request. In retrospect, it was a
bad idea to include the current request in the Pundit context. It bleeds
out everywhere and there are many contexts (in tests and models) where
we only have the current user, not the current request. The previous
commit got rid of the only two places where we used it.
