[maven-release-plugin] prepare for next development iteration
Prepare development of next minor version 4.3.0-SNAPSHOT
Remove all generated artifacts in favor of automated build
Get rid of all xtend code in favor of pure java

This commit replaces all code written with xtend with pure java
code.
Get rid of warnings in Geppetto build
[GEP-114] Drop support for Java 1.6 and below