Add output format flag

[tantalic]

Introduce a output flag to provide structured output that is more suitable for programmatic usage of command output. To be familiar to Workflow users this should be similar to the kubectl implementation: -o=<output_format>. Using -o=json should result in returning the JSON data directly from the REST API for the Controller. It might be nice to also provide YAML output (again for familiarity of kubectl users), but providing JSON alone may be sufficient.

[tantalic]

This could provide even more advanced scripting and workflow capabilities as described in issue #237.

[Cryptophobia]

This issue was moved to teamhephy/workflow-cli#18