Hardening/619 forbidden characters

### Description
o The response to 'Service not found: $URL' changed to 'unrecognized request', to avoid to respond with the data that the user supplied (security risk)
o Requests with any of the 'forbidden characters' in the values of the payload (see issue #619) are refused, both for XML and JSON.

A file with characters "invalid" means "this file is expected to fail when xmllint process it using the XSD". In this sense, this file (and all the others in this PR) should be named "valid" (as we want xmllint process it, e.g. to detect fails in the XML structure that may wrongly come in new versions).