Copyright Hygiene

Capturing an issue from a conversation I had with @jbenet at Lab Day.

We need to first document and then automate the compliance for our IP policies.

This includes:

* Preferred License
* DCO
* Commit Signing (as requested by the DCO)

I'd also add, we should use [SPDX](https://spdx.org/) compliant license info in every file, and automate the compliance of that as well.