recalculate shade of item

[maxheld83]

actually, the alpha of items shouldn't be the sd of raw scores, that's not intuitive enough.

Instead, what we would need is a distance-weighted probability or something, that tells me the probability (from 0-1!) that an item is in precisely this spot or thereabout.

That would also take care of scaling the alpha consistently, which is currently a huge problem. (the sd only has an extreme upper bound).