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/StringUtils/MA_StringUtils.cs

@@ -0,0 +1,28 @@
+//-
+
+using UnityEditor;
+using UnityEngine;
+
+namespace MA_Toolbox.Utils
+{
+    public static class MA_StringUtils
+    {
+        private const string ALPHABET = "aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ";
+
+        public static string RandomAlphabetString(int length)
+        {
+            string s = "";
+            for (int i = 0; i < length; i++)
+            {
+                s += RandomAlphabetChar();
+            }
+
+            return s;
+        }
+
+        public static char RandomAlphabetChar()
+        {
+            return ALPHABET[Random.Range(0, ALPHABET.Length)];
+        }
+    }
+}

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