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.

Because of the 'forbidden characters' inserted in the payload.
It might be that some/many of them are OK according to the XSD, but they are NOT OK according to the contextBroker.
I didn't take the time to find out which files could be 'valid'.