Improvements

[callaa]

Here is a set of improvements to Color_Preview, Gradient_Slider and Color_Dialog widgets:

• Color_Preview: A new split color mode for comparing the current color and a reference color
• Gradient_Slider can now display gradients with custom stops
• A new Hue_Slider widget (extends Gradient_Slider)
• Color_Dialog now uses the new Hue_Slider widget. The saturation/value of the hue gradient is updated along with the other gradients.
• Color_Dialog uses the color comparison mode of Color_Preview by default
• Multiple button modes for Color_Dialog:
  • "Ok/Cancel"
  • "Ok/Apply/Cancel" for semi-live editing
  • Only "Close" for live editing
• Color_Dialog now emits colorSelected when a user clicks Ok/Apply
• Alpha channel in Color_Dialog can now be hidden
• A new Color_Dialog::showColor(QColor) slot