Have a `print` function that prints out a representation of the DAG

[Kitchi]

Something like

from dagger import Dagger

dg = Dagger()

#.... add functions/layers here
#.... and here

dg.print() 
# This should produce a dotmap + some dict-like representation of the DAG

There should be a way to export the DAG structure for both visualization, and translation into other systems.

[Kitchi]

Since dagger just hooks into DAGMAN we could probably use the DAGMAN print/output functions. But if we extend to other workflow managers like SLURM, then we'll need to sort something out ourselves.