Common Workflow Language tool descriptions

[etal]

Create CommonWL "tool" interfaces for each CNVkit sub-command. Try to use these to improve integration with Galaxy and bcbio-nextgen.

Maybe wrap "batch" as a workflow instead of a tool -- not sure how this works.

Spec: https://github.com/common-workflow-language/common-workflow-language
Examples: https://github.com/common-workflow-language/workflows

[etal]

The interface generator gxargparse/argparse2cwl from the GSoC 2016 project automates this work, which is happening in the CWL repo: common-workflow-library/legacy#93