Add support for SQL databases

The goal of this branch is to add support for SQL databases using Anorm from the Play framework.

Note that I started by trying to do this with Slick instead of Anorm, but Slick depends on Scala 2.10 and it was too much scope creep to manage upgrading the whole project to be compatible with 2.10.

This branch makes SQLite the default storage mechanism. There are now no setup steps -- if you have Scala 2.9 installed and you download Zipkin, you can immediately run the daemons. Documentation for getting other SQL databases running is in `doc/sql-databases.md`.

Once this is merged, I'll look at using FuturePools to do the DB operations asynchronously, as well as adding Aggregates support.