add license queryable (#1208)

[tomkralidis]

Overview

This PR adds a license queryable (as well as updates STAC parsing of common metadata accordingly).

Related Issue / Discussion

#1208

Additional Information

Note that file tests/functionaltests/suites/stac_api/data/records.db was updated to capture license information as follows:

sqlite3 tests/functionaltests/suites/stac_api/data/records.db

sqlite> delete from records;
sqlite> .q

pycsw-admin.py load-records -c tmp.yml  -p tests/functionaltests/suites/stac_api/data  # tmp.yml is configured to repository tests/functionaltests/suites/stac_api/data/records.db
sqlite3 tests/functionaltests/suites/stac_api/data/records.db

sqlite> vacuum;
sqlite> .q

Contributions and Licensing

(as per https://github.com/geopython/pycsw/blob/master/CONTRIBUTING.rst#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pycsw. I confirm that my contributions to pycsw will be compatible with the pycsw license guidelines at the time of contribution.
• I have already previously agreed to the pycsw Contributions and Licensing Guidelines