Add a new "BaseFile" class for potential future use. This should be the "base" for all future files and folders that could exist. This is likely to change over time.
Similar to the migration of splitting DatFile into ifferent subtypes, this makes sure that logic that petains to each "type" of file that's used by SabreTools, be it an input/output archive format or a specialty file format that is treated by itself like CHDs, is in tis own namespace. ArchiveTools has been pared down accordingly and all "factory" logic should make it easier to add more formats in the future with little fuss.
