GGU-PLGW: "Save section" menu item

After selecting this menu item you can save the defined section in order to have the data available again at a later date. For reasons of clarity, it makes sense to use ".sch" as file suffix, as this is the suffix used in the file requester box for the menu item "Special/Load section". If you choose not to enter an extension when saving, ".sch" will be used automatically.