title: FIWARE: IOTAgent JSON add new atrtibute to existing device
body: <p>I have registered some devices at IOTAgent and Orion Context Broker. </p>
  
  <p>Is it possible to add a new attribute in the registered device at IOTAgent and also at Context Broker ?</p>
  
  <p>Many thanks in advance for your help</p>
  
  <p>Best Regards</p>