Issue description:
You can now specify user-defined codes for 1st and 2nd stage of double walls for Unitechnik (78) export. You can select Double wall plate that represents a structure such as a wall or roof panel
In Tekla Structures, a panel is created by picking two or more points.
(1st stage) or Double wall (2nd stage) from the Product type list in the panel user-defined attributes dialog box on the Unitechnik tab.
