Put the deepslate top texture on all sides of the block

(FYI: Grimstone was renamed to deepslate and got a slight redesign in the latest snapshot.)

Deepslate is a neat block, but I can barely tell the difference between normal deepslate and cobbled deepslate because all that changes is the top texture. I kind of wish that regular deepslate had that prettier top texture across all sides of the block, especially since people were unhappy about how much deepslate looks like bricks. It'd also fix the ore blending problem: deepslate ores use the side of the deepslate as a base texture, so when they generate on the floor they look kind of out of place.