Operation sequence visualization for MultitaskClassifier

[vincentschen]

Is your feature request related to a problem? Please describe.

It's been helpful to think about an op_sequences in MultitaskClassifier as a path through network modules for each task.
It would be great to be able to visualize this for debugging purposes!

Describe the solution you'd like

Very open-minded here — it could be cool to see everything from an ASCII print out of each op_sequence to a fully rendered graph visualization.
Implementation-wise, this could exist as a visualize_operations method or a separate MultitaskVisualizer class that accepts op_sequences upon initialization.
Open to alternatives!