Add alternate license to OBO ontology files

[cthoyt]

This repository is currently licensed under the copyleft AGPL-3.0 license, which has implications for data reuse of the ontology files, like https://github.com/jmchandonia/CORAL/blob/main/example/pedometer/ontologies/context_measurement_ontology.obo

AGPL-3.0 is also more appropriate for code than data.

I suggest adding a different license for the OBO files, e.g., from Creative Commons. CC-BY with a share-alike and/or non-commercial clause might be consistent with the government mandate mentioned in the README of this repository.

It's possible to explicitly communicate the license for an OBO file inside the file itself by adding a property_value: line to the top like the following:

format-version: 1.4
ontology:como
date: 27:08:2018 15:13
saved-by: jmc
auto-generated-by: ONTO-PERL 1.45
property_value: dcterms:license "https://www.gnu.org/licenses/agpl-3.0.html" xsd:anyURI

[Term]
id: COMO:0000000
...

(or better yet, with https://creativecommons.org/licenses/by-sa/4.0)