Scheduling Workflows

[bosonbaas]

This PR adds the ability to assign Julia functions to boxes in a workflow and then execute that workflow.

The new scheduling command has the signature:

evaluate(dwd::WiringDiagram, funcs::Dict{Symbol, <:Function}, input_vals::Array)

[bosonbaas]

This code can be more condensed by using the toplogical_sort algorithm provided for graphs in Catlab here to define the order of defining Thunks