Make it possible to grow the database (from reddit.com/top) while posting

[bgw]

Right now the bot has to grow it's database before posting. Ideally, we should always try to post, and when we've got extra API requests left over, we should try to pull stuff from /top. As thread safety is a nasty issue, I think we should use greenlet for this, or if not greenlet, some sort of system using on yield-based coroutines. @gissues:{"order":50,"status":"backlog"}