implement date according to schema

src/main/java/sensor2graph/Sensor.java

@@ -68,7 +68,7 @@ class Sensor {
 		);
 		add_attribute(body,
 			"21.T11148/22c62082a4d2d9ae2602",
-			"[{\"Date\":{\"date\":\"" + rec.get("min(all_measurements.first_msg)").asLocalDate().toString() + "\",\"dateType\":\"first measurement\"}},{\"Date\":{\"date\":\"" + rec.get("max(all_measurements.last_msg)").asLocalDate().toString() + "\",\"dateType\":\"last measurement\"}}]"
+			"[{\"dateType\":\"Commissioned\", \"date\":" + rec.get("min(all_measurements.first_msg)").asLocalDate().toString() + "},{\"dateType\":\"last message\", \"date\":" + rec.get("max(all_measurements.last_msg)").asLocalDate().toString() + "}]"
 		);
 		add_attribute(body,
 			"21.T11148/709a23220f2c3d64d1e1",