mavenize zipkin

Done by running "sbt make-pom" and tweaking a few things after.

A few notes:

- the service packages have a shaded jar created as well
  (zipkin-query-service, zipkin-collector-service, zipkin-web).
- Scrooge / Thrift sources were generated and committed to the repo
  until we get the maven plugins working for them.
- Tests aren't running yet.