make using widget tree more convenience.(fix conflict between KeyPress and Ctrl-KeyPress.)

1> add hotkey on widget tree, i - select previous item, k - select next item. 
now, you can operate on widget tree only use I,J,K,L, Ctrl and Alt key.
use "event.keysym_num == ord(event.char)" to recognise KeyPress event or Ctrl-KeyPress event.
2> set focus at widget tree after add widget. 
you do not need click on widget tree befor use widget tree hotkey after add a widget.