v2.19.0

• feat(edu): added new POST /eduResources/{resource}/createLtiLink endpoint to create LTI links from Flat for Education resources.
• feat(edu): maximum graded has been increased from 100 to 10000.
• feat(score): new nullable properties in PUT /scores/{score} to unset properties (subtitle, composer, lyricist, arranger, description, creationType, license, licenseText).
• fix(score): wrong user object in ScoreSummary, returned object has more properties than the specification (UserPublic).
• fix(spec): various properties marked as required as they will always be returned.