Use colour picker for sky colors

User Story:
As a user who enjoys creating Windlight/Environment profiles, I would like to be able to use a colour-picker in favour of RGB sliders.

Description:
Fairly simple, the Windlight/Environment editor currently requires you to enter colours as RGB components using sliders, it would be easier if we could use a regular colour-picker, and simply have the intensity (I) slider for quick adjustments.

Change the following sets of sliders to color swatches/pickers:

• Sky
  • Atmosphere
    • Blue Horizon
    • Blue Density
  • Lighting
    • Sun/Moon Color
    • Ambient
  • Clouds
    • Cloud Color