first phase of refactor to allow pluggable transports

[pyr]

The intent of this work is to have simpler ways of plugging arbitrary transports, I'd also like to move to netty for all standard transports (http, websockets, tcp, udp, graphite)

This first PR doesn't have the transport protocol realized, this would pretty quickly allow to have calls in the config such as (provided you have the transport on the classpath, more on this later):

(start-server riemann.transport.Collectd {:port 7171})

[pyr]

this says the build failed but it's time related, not related to the PR itself

[aphyr]

Awesome work pyr. Two things:

1. Can you clarify the documentation on what (setup server) does? When is it called--what's the lifecycle? Setup before start? Setup after start? Setup after stop? Any invariants we can provide here would be useful.
2. I know I'm guilty of this too, but whitespace changes in a separate commit please--just makes it easier for me to review a PR for the important bits. :)

[aphyr]

ALLLLSOOOO let me take a good hard look at that test failure for you. :) Cheers!