Highlights: improve guided laplacian

[aurelienpierre]

• Add an user-defined internal WB aiming at normalizing clipped color to white during the correction (helps recovering more magenta in fewer iterations),
• Add an exposure sanitization step after chrominance diffusion to ensure the reconstruction is at least as bright as the original. As it is, the chrominance inpainting has the potential of darkening the reconstructed areas depending on the brightness of the surrounding which helps smoothness but compresses clouds and such too much. (It only makes sense that the clipped areas should be brightened by the reconstruction).

[Jiyone]

aiming at normalizing clipped color to white during the correction

To white or other color actually.