Packaging: Update to use cibuildwheel

[rt121212121]

This task is low priority. We should look to get Nakasendo building and have it package it's own secp256k1 dynamic library which we can have bitcoinx use alternatively (which is where ElectrumSV uses it within).

This currently uses a working custom method of building for the cross-platform wheels. It would be a lot cleaner to switch over to cibuildwheel.