HSL Sliders & RGB Sliders
Feature requests:

## 1) HSL Sliders:
Currently, there's a "hue" and an "alpha" slider, I'd love to see "saturation" and "luminance" sliders.

![tab_colour_hslcolourslider](https://user-images.githubusercontent.com/16139439/29582170-54e40d44-8741-11e7-9142-b03b639d09ea.png)

## 2) RGB Sliders:
![colour_picker_sliders](https://user-images.githubusercontent.com/16139439/29582176-5839cc68-8741-11e7-82de-2c9994c51940.jpg)

