Subreddit ban list JSON: Add timestamps
Subreddit settings: update allow_top label
site_admin: Remove mergability.

This removes the prev_ fields in Subreddit.

This fixes the problem of drift if there is an error
between the wiki revision and Subreddit commiting.
/about/mod: Revert to old sorting behaviour.
ratelimit: Fix login not having ratelimit seconds field in api.
ratelimit: Do not ratelimit login if less than 3 seconds.
ratelimit: Use 429 on login ratelimit.