Created XmlReferenceDumper
Moved ReferenceDumper to Dumper\YamlReferenceDumper

This is done to make other formats, such as the XmlReferenceDumper
possible. This deprecates the old
Symfony\Component\Config\Definition\ReferenceDumper.
Modified command to support XML dumper
Modified Testing ConfigTree
Modified test
Added support for prototype values
Fixed node name of Example config
Fixed numeric values
Added tests for enum nodes
Fixed Xml dumper
Fixed Yaml Dumper