Change thumbnail appearance of presets too similar or slighly misleading.
- b)_Basic-4_Flow_Opacity : was too similar to the other flow basic presets.
- b)_Basic-5_Size_Opacity : was yet another red brush. One in ink family,
                            and other one for details is sufficient.
                            It's now yellow.
- f)_Bristles-3_Large_Smooth : The brush render a round tip on canvas, but
                               the thumbnail was displaying a flat large
                               brush. Not logic. It's now a black rounded
                               brush.
- f)_Bristles-5_Flat : 	The other way around; a flat brush-tip; the icon
                        wasn't flat enough.