Add support for SQL databases

The goal of this branch is to add support for SQL databases using Anorm from the
Play framework.

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`.

Author: @IceCreamYou
Fixes #272
URL: https://github.com/twitter/zipkin/pull/272