Incorrect placement and slabs' issue

[LongLasting]

Incorrect placement(incorrect facing):observer、piston、sticky_piston
slabs should be able to be placed when there is another slab near it with the same 'type' info, for example there are two 'smooth_stone_slab[type=bottom]' slab A is already placed, and slab B is next to it, if there is nothing under slab B, then slab B will not be placed by printer.
and, if there are a block should be 'smooth_stone_slab[type=double]', but now is 'smooth_stone_slab[type=top]' or 'smooth_stone_slab[type=bottom]' other half will not be placed by printer, we have to place it manually.