Started extracting ValueHolder from DataField.
Finished extracting ValueHolder
Added snakeyaml to dependencies, started rewriting YamlNode
Working on YamlNode, added YamlNodeSource.
Working on YamlNodeSource
Joined YamlNodeSource back with YamlNode.
Improved addChild().
Working on YamlNode
Some final (hopefully) work on YamlNode.
More work on ValueHolders - added getters with default