Put all the clients at the same level

[dlresende]

All the clients should:

• have a /ping resource that responds "pong"
• hava a /feedback resource which accepts a message {"type": "ERROR","content": "The field \"total\" in the response is missing."} and parse the same message leaving an JSON parsing example for participants
• remove all the existing parsing regarding the main problem (no more parsing for order objects and responses like Bill or other) (running the exercice with participants with a little bit of experience makes the exercice "too simple" and very short in time)
• have a test to give participants an example