Draft: Update citygml4j module to support the QualityADE version 0.1.4

This MR updates the citygml4j module implementation to support the latest version 0.1.4 of the QualityADE.

This MR is work-in-progress. Key changes and todo list:

• Automatically derive JAXB classes from the new schema using ade-xjc
• Update all ADE model classes to support the new schema
• Update ADE unmarshaller and marshaller
• Add ADE walkers for the model classes
• Update test classes and test datasets

There might still come some minor changes and tweaks to the 0.1.4 schema which would require to revisit some of the points from the above list.

Note that I have switched from Maven to Gradle because I am more familiar with Gradle. This can be undone if required before merging.