Move to centralized GitHub account

[jmorris335]

There's lots of work on constraint hypergraphs that are under different accounts. While I'm happy to host ConstraintHg under my own @jmorris335 account, I think it makes more sense to start a general CHG account (or similar) to put related projects under. This might include demos, use cases, alternate solvers, etc. The move might trigger some issue with the automated workflows, so I'll put this as a potential move in the future.