Redraw widgets on request. Add scrollbar demo.
Colors
======
backend.setcolor(name, description)
  This will parse description, prepare attributes and save them under 'name'.
  Description is in format <foreground> "on" <background> "," <attributes>.
  For example:
    "black on cyan"
    "white on cyan" or "gray on cyan, standout" (equivalent)
    "yellow on red, underline, blink"
backend.pushcolor(name)
backend.popcolor()
Default theme
-------------
menu-normal - black on cyan
menu-highlight - white on cyan
window-normal - gray on blue
window-highlight - white on blue