Display object sets on top in Treebox.
Separate GUI logick from toolkit implementation.

- OrxCraft class should deal with toolkit agnostic abstract classes for
  dialogs and widgets.
- Abstract dialogs implement all logick while toolkit dependant
  derivatoves are minimal and deal with toolkit specific plumbing.
- Introduced OrxCraftFactory class that creates toolkit specific
  implementations of Gui and DialogManager classes.
- OrxCraftFactory has to be an internal class of OrxCraft as it deals
  with Scroll implementation details and orxCraft.cpp is the only place
  it can reside.