Model groups.

Added model group support, you can now have multiple meshes in one export.
Removed OBJ and mesh replace export options.
Mesh replace didn't work, might get added again in the feature.
OBJ needs to be rewritten as well to support the multiple meshes, and Unity now has model export options in engine.
Version 1.8.0+ is now only supports Unity2018.3+.

Assets/MA_ToolBox/MA_Utilities/PrefabUtils/MA_PrefabUtils.cs

@@ -0,0 +1,41 @@
+//-
+
+#if UNITY_EDITOR
+using UnityEditor;
+using UnityEngine;
+
+namespace MA_Toolbox.Utils.Editor
+{
+    public static class MA_PrefabUtils
+    {
+        public static string CreatePrefab(string prefabName, string savePath)
+        {
+            if(string.IsNullOrEmpty(prefabName) || string.IsNullOrWhiteSpace(prefabName))
+            {
+                Debug.LogError("Invalid prefab name.");
+                return null;
+            }
+
+            GameObject gameObject = new GameObject
+            {
+                name = prefabName
+            };
+
+            string assetPath = savePath + prefabName + ".prefab";
+
+            PrefabUtility.SaveAsPrefabAsset(gameObject, assetPath);
+            UnityEngine.Object.DestroyImmediate(gameObject);
+
+            return assetPath;
+        }
+
+        public static void AddChild(GameObject prefab, GameObject child)
+        {
+            GameObject p = PrefabUtility.InstantiatePrefab(prefab) as GameObject;
+            child.transform.SetParent(p.transform);
+            PrefabUtility.ApplyPrefabInstance(p, InteractionMode.AutomatedAction);
+            UnityEngine.Object.DestroyImmediate(p);
+        }
+    }
+}
+#endif

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