- More and more refactoring of the classes and clean them up.
- Avoid memory leaks, some testing needed. Destructors are called according to
  the hierarchy of the Classes. CCombo dctor calls CAction dctor which in turn
  'delete' all buttons.
- Renamed some variables and cleaned some comments.
- Got rid of forward declarations by making one include to 'TwinPad_GUI.h' which
  in turn, includes all other header files.