block materials loading

res/content/base/block_materials/grass.json

@@ -0,0 +1,3 @@
+{
+    "steps-sound": "steps/grass"
+}

res/content/base/block_materials/stone.json

@@ -0,0 +1,3 @@
+{
+    "steps-sound": "steps/stone"
+}

res/content/base/block_materials/wood.json

@@ -0,0 +1,3 @@
+{
+    "steps-sound": "steps/wood"
+}