Add a Gradle task for generating a license-classifications.yml from ScanCode's license data

[fviernau]

Make it easy to use ScanCode's license categorization in ORT.

This can make use of https://scancode-licensedb.aboutcode.org/index.json.

[sschuberth]

Just FYI, there's already @maxhbr's somewhat similar generated https://github.com/maxhbr/LDBcollector/blob/generated/ort/license-classifications.yml for ORT. I think it would be nice to make reuse of that.

[maxhbr]

the result in https://github.com/maxhbr/LDBcollector/blob/generated/ort/license-classifications.yml contains the classification from ScanCode and other sources. (Just restricting LDBcollector to ScanCode could even produce what you look for.)

[fviernau]

Follow-up: #66.