Reorganized directory structure (third step).

- moved gensrc to src/main/java-generated.
- moved src/java to src/main/java.
- moved src/config.properties to src/main/resources/config.properties.
- moved src/log4j.properties to src/main/resources/log4j.properties.
- moved test to src/test.
- pom.xml: added build-helper-maven-plugin to support the generated source files (and added pluginRepositories element).