Update all license headers for Nextcloud 21

.mailmap

AUTHORS

apps/accessibility/lib/AppInfo/Application.php

apps/accessibility/lib/Settings/Personal.php

apps/accessibility/lib/Settings/PersonalSection.php

apps/admin_audit/lib/Actions/Sharing.php

apps/admin_audit/lib/AppInfo/Application.php

apps/dav/appinfo/v1/publicwebdav.php

apps/dav/appinfo/v1/webdav.php

apps/dav/appinfo/v2/remote.php

apps/dav/lib/AppInfo/PluginManager.php

apps/dav/lib/BackgroundJob/CleanupDirectLinksJob.php

apps/dav/lib/CalDAV/BirthdayService.php

apps/dav/lib/CalDAV/CalDavBackend.php

apps/dav/lib/CalDAV/Reminder/INotificationProvider.php

...ib/CalDAV/Reminder/NotificationProvider/EmailProvider.php

apps/dav/lib/CalDAV/WebcalCaching/RefreshWebcalService.php

apps/dav/lib/CardDAV/AddressBookImpl.php

apps/dav/lib/CardDAV/CardDavBackend.php

apps/dav/lib/CardDAV/Converter.php