Comment: hide gildings + distinguished if removed
Suggest title: support og:title meta tag
Archiving: support custom age cutoff per-subreddit

This consolidates the three previous globals of REPLY_AGE_LIMIT,
VOTE_AGE_LIMIT, and REPORT_AGE_LIMIT into a single timeinterval setting
of ARCHIVE_AGE, and allows individual subreddits to use an archive_age
attr to override this default cutoff.