Grass And Dirt Slabs

Adds slabs for all grass/dirt/mud blocks in the game.
When you stack the slabs to make a whole block, that block will have the top face texture on all faces.

The slabs are crafted through the Builder's Workbench using their respective full blocks

List of current issues with the mod (probably wont be fixed):

• Slabs that change appearance depending on the biome will have weird-looking dirt.
• Blocks using draw type "Model" seem to be shaded very differently from blocks using draw type "Cube", or that's what it seems like anyway. This led me to shade certain faces myself, which led to them still being differently shaded, but not as much. This also means that rotating and placing the slabs will look pretty weird, but still works.
• It seems like slabs cannot have transition textures (I'm assuming this is because they use the "Model" draw type instead of "Cube"). They will however have transition textures when they are stacked and turned into whole blocks.