[FEATURE] Add saturation control for raster images
[FEATURE] Option to convert a raster to grayscale with choice of desaturation mode (lightness, luminosity, average) (fix #5837)
[FEATURE] Add colorize control for raster layers
Add strength slider for raster colorization
Fix initial state of saturation controls
Merge remote-tracking branch 'origin/master' into hue_saturation
Fix branch to apply to current master
Merge pull request #480 from nyalldawson/hue_saturation

Add hue and saturation controls for raster layers