Fix scaleColor and adjustColor from ColorUtils

Both methods had multiple issues:
- Both methods were reading Color::value() but then reassigning the
  updated value to Color::setHsl() instead of Color::setHsv().  This was
  leading to very different colors than expected.
- Next, adjustColor was applying any passed alpha value as absolute
  value for the new alpha instead of applying it as a delta, which is
  what happens to all the other properties.
- The alpha adjustment for scaleColor is now applied separatly, so it
  also gets applied if rgb deltas are specified, and not only with hsv
  values.