replace log4j2.properties with log4j2.xml

The properties support for log4j2 is not well documented and
possibly buggy. I couldn't figure out how to change the log
level of a logger.

pdb-ui/src/main/resources/application.properties

@@ -4,4 +4,4 @@ db.base=${base.dir}/db
 path.tmp=${base.dir}/tmp
 path.output=${base.dir}/out
 
-logging.config=classpath:log4j2.properties
+logging.config=classpath:log4j2.xml