Move blockIp and blockEmail to SQS messages (fix #27)

I've just fixed that in the last push.

I tried to make handleBan return promises in `bans/handler.js` but I wasn't sure how it would interact with the non-promisified EventEmitter. In the end, I just promisified the function itself to fix the issue in the PR while ignoring the larger issue of a lack of Promises elsewhere.