Get KafkaProducer working

This is a rewrite of parts of datasift#19.

I tried to stick to the existing conventions used by KafkaConsumer when it comes to config property names, getters/setters and annotations. (Although we did note that, with newer versions of dropwizard and jackson at least, Jackson serialization can be done with a lot less boilerplate than is used here.)

I also included a commit which fixes some typos (in setter method names) and inconsistencies in KafkaConsumer -- can separate this out if you want but wouldn't hurt to merge too.

Cheers!