Allow subreddits to hide comment scores initially

Adds a new subreddit setting that allows defining a period
of time after posting that comment scores will be hidden.
Add <category> to rss data where relevant
Add indicators of hidden score to API and HTML

If the score is hidden, data-ups and data-downs will both be 0, and
the comment will also have the "score-hidden" class
Add "[score hidden]" marker

Includes tooltip with info about the length of the hide period