Move code to named package
Remove managedSourceDirectories modification

This fixes adding correct directories to Idea project files with
sbt-idea. Plugin authors should not modify managedSourceDirectories
directly, but only provide sourceGenerator which generates sources
under a subdirectory of 'sourceManaged' as described here:
http://www.scala-sbt.org/0.12.3/docs/Howto/generatefiles.html
Merge branch 'topic/generated_sources_path'