Fix Bug 723: Remove VK_KP_<Cursor> numpad key-codes, use general VK_<Cursor> key-codes; Respect numpad printable keys; Use keySym for numpad if possible.

- KeyEvent keyCode/keySym values re-ordered!

- Remove VK_KP_<Cursor> numpad key-codes, use general VK_<Cursor> key-codes.
  Numpad cursor keys are not supported on some platforms (Windows),
  or not configured on most X11 configurations.

- Respect numpad printable keys,
  i.e. don't treat them as non-printable.

- Use keySym for numpad if possible.
  Numpad keys require modifiers, hence X11 and Windows shall return keySym.