legal: setup contributor license agreement

[ahdinosaur]

this is maybe controversial, but i'm keen for a contributor license agreement! at the moment everything is licensed under AGPLv3, but that means we can only change the license given the consent of all the copyright contributors. in case we want to re-license to another license in the future (like if we want to play with License Zero), i'm keen to be the sole copyright owner (until we have a legal entity who will own the copyright), which means contributors will need to assign copyright to me (or the legal entity).

[ahdinosaur]

(keen to follow along with root-systems/cobuy#77)

http://contributoragreements.org/ca-cla-chooser/

options chosen:

Option	Choice
Entity Name	Michael Williams
Project Name	ButtCloud
Project Website	buttcloud.org
Project Email	hello@buttcloud.org
Contributor Signing Process Address	http://buttcloud.org/cla
Project Jurisdiction	California
Agreement Exclusivity	exclusive
Outbound License(s)	Not Applicable
Documentation License(s)	____________________
Patents	Traditional Patent License