sampling multiple pixels and averaging the results

[globglob3D]

I'm not a c++ programmer so if anyone want to finish this please go ahead because I most likely won't.

This add a feature to sample multiple pixels near the crosshair. This is very useful for sampling noisy images where the color variation per pixels is important but what you want is the overall color of an area of the image. Other softwares like PS have this feature.

What's left to do (basically 90% of the work, sorry) is to turn it into an option with the ability to choose the amount of sampled pixels (in a circle around the crosshair). Adding a visual indicator like a circle line around the crosshair would be beneficial to the UX as well.