GGU-SLAB: "Define nodes" menu item

Using this menu item, the triangle nodes for the constrained modulus profile mesh can be defined by mouse click. Nodes are defined using the left mouse button and deleted using the right mouse button. In terms of the constrained modulus profile the new nodes are allocated to the layers with the standard depths, as previously defined using "Constrained mod./Layers" and "Constrained mod./Default depths" menu items.