Separate HistoricLoad from LegacyLoad

[BenCheung0422]

This depends on #610. It is well-known and obvious that both Save and Load, even LegacyLoad are messy and chaotic. I separate the part of version loading that is not indicated by versioning. With my investigation, world save versioning is added in 1.9.1, but save system is implemented earlier, which means there are certain versions that there are no version indicators. Then, I reorganize to check the history and to clearly write a new loading mechanism for it. Ideally, this method could be beneficial for all loading behaviour, but it is a kind of more works to do, and I do this is just for the part of #581. A on-demand auto data fixer is included.