Improvements and fixes

[frengor]

This PR makes some improvements and fixes. The major ones are:

• Handle classifier during transitive dependency resolution
• Allow null classifier in Library builder: by default the classifier is already null, but null wasn't a valid classifier when calling the .classifier(...) method
• Add missing settings to JSON configuration: adds the possibility to configure all the properties of a Library from the JSON file
• Rename JSON group and name for consistency: now groupId and artifactId are used in the JSON instead of group and name
• Replace prints to System.err with proper logging
• Throw exception rather than only logging the error when loading from JSON file
• Now all the fully qualified names of classes inside strings have the dots replaced with {} to avoid issues with relocations