XmlDocument() memory leak

[AnthonyZJiang]

Issue: Memory usage can become hugh (>1G) once a big savegame is loaded. It gets doubled when edits are being saved to savegame. This memory, however, is only released after the application is closed.

Cause: The LSX content loaded using XmlDocument().Load does not get disposed properly after all references to the object are destroyed.

Possible fix: use XmlRead instead of XmlDocument.