Merge pull request #14 from broadinstitute/irwin-trimmomatic

Irwin trimmomatic
Merge branches 'irwin-taxon_filter' and 'master' of github.com:broadinstitute/viral-ngs
Merge branches 'master' and 'irwin-taxon_filter' of github.com:broadinstitute/viral-ngs into irwin-taxon_filter
Merge branch 'master' into irwin-taxon_filter
DownloadPackage now uses relative path, defaults to build dir, has post_download_command, and handles .bz2. Removed DownloadScript.
Added tools for picard and samtools.
Include picard and samtools in testtools.