[API] Workflow & Parametrization Design

[ryanhammonds]

The workflow design could be simplified. It currently has a complex sub-classing system, e.g.

class WorkFlow(BIDS, Simulate, Transform, Model): # <- simplify?

This design creates a confusing web of class methods and attributes, but at the same time isolates the implementation of components. There's probably a better design option. At least the current implementation could be cleaned up / polished / better organized / etc.

The parameterized workflow design was developed in a rush to get something working. Re-writing (partially) could be beneficial or at least more robust tests + benchmarking to ensure no computation bottlenecks.

Re-designing the Workflow class and workflow parametrization could be useful if planning on additional development or support.