wxGUI: import missing module

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@37857 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/gui_modules/nviz_tools.py

@@ -18,6 +18,7 @@ for details.
 
 import os
 import sys
+import copy
 
 import wx
 import wx.lib.colourselect as csel