Make gctree deterministic when ranking is degenerate

[willdumm]

Adds a --seed argument to the inference cli, and fixes an issue where inference results could be nondeterministic with degenerate ranking criteria.

[willdumm]

This PR requires historydag v1.0.1, which isn't released yet, but will include a fix to make dag node orderings consistent across runs and after copy.
matsengrp/historydag#22

I'm still seeing some strange behavior that I don't think I'll be able to explain:
If I install the fixed version of historydag, and install stock gctree v4.0.4, that fixes the issue where internal node names differ between runs.

If I then install the same gctree code with pip install -e (after doing git checkout v4.0.4), internal node names are still consistent between runs, but different than with stock gctree v4.0.4 from PyPI. Why, I don't know.

What I am confident in though, is that the changes in the above-referenced historydag PR make internal node names consistent between runs. The changes in this PR

• require the fixed historydag version, and
• allow setting a random seed from the command line interface.