unify license headers for public API files

lib/public/activity/iconsumer.php

lib/public/activity/imanager.php

lib/public/api.php

lib/public/app.php

lib/public/appframework/controller.php

lib/public/appframework/http.php

lib/public/appframework/http/jsonresponse.php

lib/public/appframework/http/response.php

lib/public/appframework/http/templateresponse.php

lib/public/appframework/iapi.php

lib/public/appframework/middleware.php

lib/public/authentication/iapachebackend.php

lib/public/config.php

lib/public/db.php

lib/public/defaults.php

lib/public/files.php

lib/public/files/alreadyexistsexception.php

lib/public/files/entitytoolargeexception.php

lib/public/files/file.php

lib/public/files/folder.php