Modify IO chapter to use previous build structure.

* Remove Build.scala file.
* Modify eveyrthing to be build.sbt
* Move sources into appropriate directories for subprojects.
* Move all the IO uber jar settings into website/build.sbt
* Set exportJars := true so dependent projects show up as JAR files.
* Add uniqueness forcing for the uber JAR file.
* Fix start class to be play's server class.