[pjforhdq] Touchscreen overlay keyboard

For a touchscreen keyboard with a very small number of buttons (4 to 9, e.g., Morse code), the keyboard may be overlaid on to the content.  This would be useful for small displays (e.g. smartphones).  The human is expected to have memorized the buttons, or we use transparency tricks to show both the content and the keyboard (if the latter, then more than 9 buttons are OK).  This also requires that the content itself not have any touch sensitive areas. Would work well for command lines.