Update copyright attribution

[gonuke]

The current copyright message in conf.py only includes CNERG - this should change.

[abachma2]

We should probably change the copyright to individual authors as opposed to research groups. It would up to each contributor to make sure they are on the authors.rst file for each project they contribute to, but we can start by looking at the PRs in each repo. We could also automate emails to remind contributors to add themselves to the authors list when they make/merge their first PR.

[abachma2]

Did we still want to change this? What should it be changed to?

[gonuke]

I wonder if we can change it to "Cyclus Ecosystem Contributors" with a link to here : https://fuelcycle.org/#contributors