Added undo for delete button

lang/en/home.php

@@ -140,4 +140,6 @@
     $g_lang["traversal_order"]  = "Traversal order: ";
 
     $g_lang["curve_edge"]       = "Edge bend";
+    $g_lang["undo"]             = "Undo";
+
 ?>

lang/ru/home.php

@@ -143,4 +143,5 @@
     $g_lang["traversal_order"]  = "Порядок обхода: ";
 
     $g_lang["curve_edge"]       = "Изгиб дуги";
+    $g_lang["undo"]             = "Отменить";
 ?>