Major code refactoring.

* Renamed package to peel.
* Added hierarchical configuration for systems based on Typesafe Config package.
* Added SystemConfig abstraction on top of the hiarchical configuration.
* Implemented HDFS, MapReduce, and Stratosphere systems.
* Added a DataSet bean responsible for providing the experiment's datasets.
* Integrated Argparse4J into the frontend.
Added sample fixtures.template.xml and fixtures.wordcount.xml to peel-sketchbook.
More robust start up routintes for all systems.
Updated 'system.default.java.home' for cloud-7.
Refactored DataSet beans.

* Added FileSystem trait.
* Converted StaticHDFSDataSet to generic StaticDataSet.
* Fixed two small bugs in the MapReduce and HDFS startAndWait() methods.
Implemented ExperimentRunner for Stratosphere.
Fixes in the fixtures.*.xml files.
Simplified peel.sh.
Fixed a bug with DOP per node in Stratosphere.
Implemented lazy systems set up.
Added version-specific system config templates.