Guidelines alignment (errors and camelCase)

[monamok]

A new PR will be open order to align the API definition with following changes in the guidelines:

• Parameters should be named in lowerCamelCase. Issue, Discussion & PR.
• Adjust the schema references in the errors responses and apply the agreed solution: Issue & PR.

I removed the restriction for error status as in commonalities there is no agreement about limiting the integer values.

PR#22

[monamok]

Done