fixed null sourceId for xml parsers, attribute renamed to @id

src/main/java/de/sekmi/histream/io/XMLObservationParser.java

@@ -178,7 +178,7 @@ class XMLObservationParser extends AbstractObservationParser{
 
 	protected void parseSource(AttributeAccessor atts){
 		setMeta("source.timestamp", atts.getValue("timestamp"));
-		setMeta("source.id", atts.getValue("source"));
+		setMeta("source.id", atts.getValue("id"));
 	}
 	protected void parseEncounter(AttributeAccessor atts){
 		encounterStart = DateTimeAccuracy.parsePartialIso8601(atts.getValue("start"));

src/test/resources/dwh-eav.xml

@@ -3,7 +3,7 @@
 	<meta>
 		<!-- Zeitpunkt, an dem der Export erstellt wurde bzw. Datenstand -->
 		<etl strategy="replace-visit" />
-		<source timestamp="2015-04-21T08:58:00" system="test"/>
+		<source timestamp="2015-04-21T08:58:00" id="test"/>
 		<enum concept="L:46098-0">
 			<value id="0">Male</value>
 			<value id="1">Female</value>