Add missing textures and models from Chorus' Version

This also helps in preparing for the Nether Update (1.16). Textures were
optimised using OptiPNG by:

optipng -o7 -nx

followed by a second run with the defaults.

assets/minecraft/blockstates/cut_sandstone.json

@@ -0,0 +1,10 @@
+{
+    "variants": {
+        "": [
+			{ "model": "block/cut_sandstone" },
+			{ "model": "block/sandstone/cut/normal/1" },
+			{ "model": "block/sandstone/cut/normal/2" },
+			{ "model": "block/sandstone/cut/normal/3" }
+		]
+    }
+}