Major refactoring for v3.0.0

- App.java isn't scary anymore! :trollface:
- Support defaults, UDP defaults and TCP defaults
- Move the Kafka config into Typesafe Config
- Kafka client IDs for every listener
- Stats per listener

Closes #22, #24, #29.
Handle, log and count exceptions parsing multipart headers
Crude filters support

Once improved and tested, should close #23.