Added support for generated datasets.
Updated peel-sketchbook scripts.
Fixes in the generated dataset logic.
Minor fixes:

* Proper exit on failed Job execute().
* Better error handling if system archive is missing.
* Added hadoop paths section in hadoop-env.sh for Hadoop 2.
* Simplified formatting logic for HDFS 2.
Core package improvements:

* Added sys:setup and sys:teardown commands.
* Fixed a bug in the DependencyGraph reverse method.
* Added 'app.path.downloads' parameter to reference.conf.
Added Zookeeper system.