Add metadata to LASSY for anonymization

[JeltevanBoheemen]

Anonymization is performed on CHAT input files, and a %xano-tier is added for utterances with anonymizations.
Add these to the LASSY treebank file as metadata elements. This can be achieved using sastadev.metadata.Meta. This class has a toElement method that converts the generated metadata element to an lxml.etree.Element.

Figure out a good moment to perform this. Preferably after the parse, and before correction is performed.