Rewrite ForceVariableDialog. It's not based on wx.TextEntryDialog

Don't customize standard wx.TextEntryDialog on the fly, implement your
own dialog for that with expected behavior and without any hacks.

<?xml version='1.0' encoding='utf-8'?>
<ModbusServerNode xmlns:xsd="http://www.w3.org/2001/XMLSchema" Local_Port_Number="1502" Local_IP_Address="127.0.0.1"/>