If there is an exception when copying / moving stems/groups the user does not see an appropriate error message

When attempting to copy a group to a stem where the user has insufficient privileges no error string is printed to the screen. The API method which throws the exception does have a meaningful error message, however, it is hard coded in English. I believe that all the copy / move actions will have the same problem.

For the time being I will modify NavExceptionHelper to use the hard coded exception text, but we should look again at how API exception messages are handled.