Changeset 18164

#3136

• fixed a bug in StructureTemplateView -> only nodes of type SubFunctionTreeNode are selectable
• added a way to keep old sub functions after parsing a new expression
  • overwrote some basic object methods for SubFunction to keep it simple
  • only old sub functions, which match the name and signature of the new ones, are saved; examples:
    • old: f(x), new: f(x) -> keep old
    • old: f(x1), new: f(x1, x2) -> use new
    • old: f1(x), new f2(x) -> use new