Investigate using BPML

Angel, one of the panelists at the hackathon, suggested we look into using [business process markup language](https://en.wikipedia.org/wiki/Business_Process_Modeling_Language) for workflow definitions, as it's rather well-established, and has tools out there that would likely be compatible ([example tool](http://demo.bpmn.io/))

Start by reading the linked Business Process Modeling Language overview and inspecting the example BPMN tool to understand the proposed format and compatibility target. Define the scope of adopting BPML for workflow definitions and identify what a complete integration would need to demonstrate; the issue names no files or tests.

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