Feature/http status code string converter

### Description
Two minor changes
1. Added a function to convert a HttpStatusCode to an ASCII string.
    This function should be used everywhere instead of hardcoding the values.
    Especially the StatusCode constructor (ErrorCode will soon be removed) should accept
    only two parameters, "HttpStatusCode code" and "std::string details", as reasonPhrase will be taken from
    the output of 'code' sent to this new function.
2. The name of the XSDs has changed so our xmlCheck scrip had to change as well.