Changed to use dbp_domain and dbp_param_decode_U to fix an i18n issue that response data was empty

The problem is that a response is empty when a user accesses to /data when the dbp_domain is not the English chapter and/or datasets use IRIs. 
This pull request fixes the second issue on https://github.com/dbpedia/dbpedia-vad-i18n/issues/1.