Groovy upgrade and commons-logging+log4j replaced by slf4j+logback

Hello all,

I made a few changes to code. 
1.) upgrade to Groovy 2.3.9 => this fixes a log of unit-tests
2.) removed compile dependency on log4j => it's not requiered for compilation/runtime
3.) removed dependency on commons.logging => one logging facade ( slf4j ) has to be enough
4.) changed project version to 1.4.2.6-SNAPSHOT => because of new version of artifact

please review it

bye 

vlk