First commit for GA4GH common classes and Picard runner

It's nice to see the addition of GATK with pipeline integration - it will definitely open up a lot of possibilities.  

On another note, I'm not sure that the following location is working properly yet:

ga4gh://www.googleapis.com/genomics/v1beta/reads/16801540936334623823/CLqN8Z3sDRDQldHJ_rTS9VE/1/