OScope__ClearScreen (ul_pbar_graphics)

 *  Synopsis:
 *    #include <ul_pbar_graphics:oscope.h>
 *
 *    TOScope__Result OScope__ClearScreen( void )
 *
 *  Function intent:
 *    OScope__ClearScreen() clears and redraws the entire oscilloscope display.
 *  Function parameters:
 *    none
 *  Function return value:
 *    CBS_OK            success
 *    CBS_NOSETUP       OScope__DisplayScreen() not yet called
 *    else              wn_xxx() function error occured