Right now, the filter pages have images for their gui, but there's no...

• indication of when they're useful (There's a handful of filters which are genuinely useless).
• Not enough images to show their effect.
• There's no explanation or mention of filter-presets.

Aso we need to add Gradient map and Normalize to 'map', add 'use normal map' to the phongbumbmap filter and add hsi/hsy/ycrcb to the hsv adjustment filter.