This is a major change to the way block metadata is handled within the PM core. This separates variant metadata (which really ought to be part of the ID) from state metadata, and in a couple of cases flattens separate states of blocks together.
The result of this is that invalid variants can be much more easily detected, and additionally state handling is much cleaner since meta is only needed at the serialize layer instead of throughout the code.
the count parameter is useless since Item ctor should now only be used for constructing item _types_, not actual items. All item creations for inventories etc, should go through the ItemFactory.
