add API to get hologram item

Author: Glease

src/main/java/com/gtnewhorizon/structurelib/StructureLibAPI.java

@@ -86,7 +86,7 @@ public static void disableInstrument() {
 
     /**
      * Check if instrumenting is enabled.
-     * 
+     *
      * @return true if enabled, false otherwise
      */
     public static boolean isInstrumentEnabled() {
@@ -272,6 +272,13 @@ public static Item getItemBlockHint() {
         return StructureLib.itemBlockHint;
     }
 
+    /**
+     * Get the hologram item.
+     */
+    public static Item getDefaultHologramItem() {
+        return StructureLib.itemConstructableTrigger;
+    }
+
     /**
      * Check if structure debug mode is on.
      *