Forced anonymity hours

Allows a number of hours per day (distributed semi-randomly) to have forced global anonymity. No names or tripcodes are written to the database at the time.
How about putting these in `forced_anon/server.js` instead, and then doing something like `if (config.ANON_HOURS) require('../forced_anon/server');` instead, similar to https://github.com/bakape/doushio/blob/anon-hours-pr/server/server.js#L30?