fix caves issues & add block 'surface-replacement' property

src/content/ContentLoader.cpp

@@ -286,6 +286,7 @@ void ContentLoader::loadBlock(
     root.at("hidden").get(def.hidden);
     root.at("draw-group").get(def.drawGroup);
     root.at("picking-item").get(def.pickingItem);
+    root.at("surface-replacement").get(def.surfaceReplacement);
     root.at("script-name").get(def.scriptName);
     root.at("ui-layout").get(def.uiLayout);
     root.at("inventory-size").get(def.inventorySize);