DATAJDBC-201 - Reduced logging for builds.

Set logging level to WARN.
Removed a System.out call.

The detail loggers are still in the logback.xml as comments to be used for debugging and demonstration purposes.

src/main/java/org/springframework/data/jdbc/core/conversion/JdbcEntityWriter.java

@@ -99,7 +99,6 @@ public class JdbcEntityWriter extends JdbcEntityWriterSupport {
 
 		aggregateChange.addAction(insert);
 		referencedEntities(insert.getEntity()) //
-				.peek(System.out::println)
 				.forEach(pav -> insertReferencedEntities( //
 						pav, //
 						aggregateChange, //