Generalize AdamBasicTask for any ADAM command. Closes #13

[jfeala]

Hey Uri,

Let me know if this is along the lines you were thinking with #13. This works on spark-ec2 (Spark 1.3/Hadoop 2.6) for the included example workflows and for toaster.py with test/test-genotypes.json, but I'm still debugging some strange behavior for test-alignments.json.

I can also expose executor-memory in a separate PR if you only want that piece of the code.

Changes:

• Factor out reusable ADAM CLI task class
• Add example workflows using ADAMBasicTask base class
• Expose executor-memory flag to spark-submit