code: public boolean moveRasterLayerDown(RasterLayer layer) {
  		int position = getLayerPosition(layer);
  		return position >= 0 && moveRasterLayer(layer, position - 1);
  	}
docs: Move a raster layer down (=back) one place. Note that at any time, all raster layers will always lie behind all
  vector layers. This means that position 0 for a vector layer is the first(=back) vector layer to be drawn AFTER
  all raster layers have already been drawn.
  
  @param layer
  The raster layer to move more to the back.
  @return Returns if the re-ordering was successful or not.
  @since 1.8.0