EMI: Parse sprite Z offset.
EMI: Always write sprites to the depth buffer.
EMI: Do not disable writing to color buffer if an actor's sort order is >= 100.

Fixes invisible Guybrush in the set unc.
EMI: Sprite blend mode byte value 7 should give additive blending as well. FIXME: Probably a flag field

This value is used for the ship masks in the set shi.
EMI: Fix parsing of sprite flags. TODO
EMI: Make variable naming more descriptive in Sprite.