I add a new FX_MODE "Rainbow_Static"

[Richi]

To draw a static rainbow over all the LEDs whitout running/blinking/chasing, only Static.

/*

• Rainbow whitout running function
  */
  uint16_t WS2812FX::mode_rainbow_static(void) {
  for(uint16_t i=0; i < _seg_len; i++) {
  uint32_t color = color_wheel(((i * 256 / _seg_len) + _seg_rt->counter_mode_step) & 0xFF);
  setPixelColor(_seg->start + i, color);
  }
  return _seg->speed;
  }