Export very large Wiki to disk

This wiki export application supports:

export in a folder (not packaged as xar)
very large wikis
documents with a very large number of attachments
old XWiki/Groovy version that:
- does not handle java method override properly (things like write(Element element) and write(Node node) where Element extends Node)
- does not support space APIs (getSpace(), setSpace(), etc.) (it's generally web in old APIs)
attachments version are not exported, way too buggy in old versions (and certainly in new too)
make sure to write the XML file with the proper encoding
some workaround for some MySQL bug around too large number of documents and "distinct" keyword i had issue with