KisPaletteView was in kritaui, which depends on kritawidgets. There are also several widgets in kritawidgets that have their own implementation for GUI of a palette. This revision moves KisPaletteView into kritawidgets so that these widgets can use it. This way, in future modification in the palette (or the color set), fewer work would be needed.
The next step is to modify these widgets so that they use KisPaletteView instead of their own implementations.