Module which has utilities for core models, particularly URNs.

This is a separate module from core-models due to a technical restriction. Everything in core-models is already defined at LinkedIn, we have essentially forked it in open source. So when we build internally, we need to actually ignore core-models, and use the internal definitions instead. So for anything that isn't forked, i.e. these utilities, it needs to go into a separate module, or it would break LinkedIn's build, as they would be "missing".