extended logging (log4j), refactoring

switched to log4j-logging and extended logging of debug-informations;
internal refactoring
replaced slf4j with log4j, integrated PMD4.0.1

depends now on pmd-eclipse-plugin 4.0.1 because of problems with 4.0.0;
removed dependency on slf4j 1.6.1 and added dependency to log4j 1.2.15