Conf. Conversion Tool: some tags/attributes still are not properly serialized

1. The async element of the singleFile or store tag is enabled in the serialized XML, even if it is disabled in 6.0 config xml (leftover from JDG-387). Empty write-behind tag appears which enables the async for the store.
2. The l1 tag is not serialized to new version (leftover from JDG-351).
3.The global site element is not serialized to new version (leftover from JDG-381).