Fix missing @since tags in OCP

lib/public/appframework/db/doesnotexistexception.php

lib/public/appframework/db/entity.php

lib/public/appframework/db/mapper.php

...blic/appframework/db/multipleobjectsreturnedexception.php

lib/public/defaults.php

lib/public/files/folder.php

lib/public/files/locknotacquiredexception.php

lib/public/iuser.php

lib/public/iusermanager.php