Add UI support for blending range parameter

[matham]

By default, when fusing tiles, only 40 pixels around the border of tiles are blended together. In my case, I often have much more overlap and so blending of 40 still leaves pretty clear boundaries between tiles. So I added a parameter that controls how many pixels are blended. I typically set them to like 500-1000.

I'm attaching images below to show the difference blending 40 vs 500 or even 1000 pixels make to my fused brain.

I have tried intensity adjustment, but it is still not enough to overcome the lack of blending. The images I'm including are fused lightsheet images taken using a 488nm, 561nm, and 640nm laser. And in them I try different blending values and different lambda values for intensity adjustment.

It isn't clear to me if there's a downside to simply setting the blending to a very large value, like 5000. But I figured adding it as a option is better.

488nm images
561nm images
640nm images