Gxformat2

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* Validate Galaxy Markdown in workflow reports as part of linting.
* Improved null handling in native ga workflow linting.
* Enhancements to workflow linting from Python. Lint for lack of documentation,
tools using the test toolshed, and implement special linting for training
material workflows to ensure a tag matches the workflow topic.
* Add gxwf-viz script that produces a cytoscape visualization of a workflow.

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* Bug fix to handle outputs without labels in Format 2 - they
don't validate per se but they are important for testing in the
Galaxy framework.

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* Implement scheam, validation, linting (for Format 2 and .ga).
* Handle new reports field in Galaxy 19.09 workflows.
* Numerous fixes for conversiion to and from native workflows.
* Numerous new test cases.
* Implement Java project for valiating and linting both kinds of workflows.

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* Implement default values in gxformat2.

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* Fix output IDs of 0.

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* Implement set_columns PJA.

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