Layout constraint lost on .convert and Gamut v4

[p0nce]

        image.setLayout(LAYOUT_GAPLESS | LAYOUT_VERT_STRAIGHT);
        image.convertTo(PixelType.rgb8); // if there is a conversion, then the above constraints are lost, because there is no LAYOUT_KEEP by default

breaks expectations

[p0nce]

Actually very annoying!

• [ ] Create LAYOUT_KEEP constant
• [ ] Any public call that manipulates storage preserves layout constraints by default (but of course, no content outside of valid area such as borders)

This will be for a next major tag.