Added `minimize` and `unMinimize` to Window class.

This allows to focus a window when it's minimized.

Example:

bind "M", mash, ->
  for w in api.allWindows()
    if w.title().indexOf("mutt") != -1
      alert w.title()
      if w.isWindowMinimized()
        w.unMinimize()
      else
        w.focusWindow()