GATK4 branch does not require separate Picard

[jdwheaton]

The GATK4 jar has all of the Picard tools integrated, so it is no longer necessary to include a separate jar for Picard in the docker image nor to use the old command syntax which differs from the new GATK4 style.

I have made these changes in a local repository and can submit a PR if you'd like.

[pditommaso]

Nice! A PR is very welcome.

[jdwheaton]

No problem.

Solved in #15

[pditommaso]

Merged. Thanks again!