Rewrite dataset code in Julia

[jopetty]

I think it would make sense to use Julia (or something like it) to generate datasets instead of Python. There's more robust support for working with algebraic objects in Julia than in Python, which would

• potentially mean faster generation for large groups, and
• allow us to construct more exotic groups than direct products of Sn/An/Zn

It looks like GAP.jl might be promising?