More options for create grid (especially standard deviation grid)

[andyroo]

After working with dense pointcloud editor in 1.0 beta, I wanted to bring this up again - I mentioned it before, but lumped it in with other things.

Being able to generate a standard deviation grid with the same cell extent as a DSM would be very useful for removing noise in orthoimages. I could use the STDev grid to constrain which cells in the DSM get interpolated from surrounding cells, or assigned a lower weight in focalmean smoothing operations.

And of course it would be amazing to be able to do other operations on the points within a cell, and output those results to a grid. I would love to be able to calculate things like min, max, range, arithmetic mean, geometric mean, median (I think that might be what's output already?), etc.)

But especially standard deviation.