Update the license headers for Nextcloud 20

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apps/accessibility/lib/AppInfo/Application.php

.../accessibility/lib/Controller/AccessibilityController.php

apps/accessibility/lib/Controller/ConfigController.php

apps/accessibility/lib/Service/JSDataService.php

apps/admin_audit/lib/Actions/Sharing.php

apps/admin_audit/tests/Actions/SecurityTest.php

apps/cloud_federation_api/lib/AppInfo/Application.php

apps/comments/lib/Capabilities.php

apps/comments/lib/JSSettingsHelper.php

apps/comments/lib/Listener/CommentsEntityEventListener.php

apps/comments/lib/Search/CommentsSearchProvider.php

apps/comments/lib/Search/LegacyProvider.php

apps/comments/lib/Search/Result.php

apps/comments/tests/Unit/Activity/ListenerTest.php

...omments/tests/Unit/Collaboration/CommentersSorterTest.php

apps/comments/tests/Unit/EventHandlerTest.php

apps/comments/tests/Unit/JSSettingsHelperTest.php

apps/dav/appinfo/v1/webdav.php

apps/dav/appinfo/v2/direct.php