experiment gradle-nexus-plugin
improve pom.xml :
- harcode version (eg 3.0.10 vs 3.0.0+date)
- restore groupId to com.jme3 (why not org.jmonkeyengine ??)
- add developers info into pom.xml
use plugin maven-publish (instead of maven)
- remove nexus plugin
- publish javadoc and sources for jme3-core