Add support of SDMX error codes

[charphi]

Example:
https://registry.sdmx.org/ws/rest/data/ESTAT%2CNAMAIN_IDC_N%2C1.10/A.N.AL.W0.S1.S1.D.P3._Z._Z._T.XDC.LR.N/all

HTTP response code: 404
HTTP response body:

<?xml version="1.0" encoding="UTF-8"?>
<mes:Error xsi:schemaLocation="http://www.sdmx.org/resources/sdmxml/schemas/v2_1/message https://registry.sdmx.org/schemas/v2_1/SDMXMessage.xsd" xmlns:mes="http://www.sdmx.org/resources/sdmxml/schemas/v2_1/message" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
	<mes:ErrorMessage code="100">
		<com:Text xmlns:com="http://www.sdmx.org/resources/sdmxml/schemas/v2_1/common">No data for dataflow: urn:sdmx:org.sdmx.infomodel.datastructure.Dataflow=ESTAT:NAMAIN_IDC_N(1.10)</com:Text>
	</mes:ErrorMessage>
</mes:Error>

[charphi]

First step in 160c327