continuous attribute slider filter and threshold

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The main parts to this:

• toggle between a threshold slider and a mask slider
• create filter from mask
• create filter from threshold

Toggle between threshold and mask

• default to Mask?
• radio buttons: Threshold/Mask

Filter from mask:

• the old behavior of filtering with the greyed out areas excluded

Filter from threshold:

• Rather than exclude the high and low values and creating a binary attribute from a continuous filter, create a 3-category attribute as follows: Fairly typical in bioinformatics: Low = blue (cold). High = red (hot) Medium = something in between (like purple) --Josh
• Use blue-black-red on white background, blue-white-red on black background

A related bug is at #38

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from Josh: The slide is a cutoff that sets a floor and ceiling, much like image editing software. What you're effectively looking at now is a coloring where bright says anyone past that rightmost slider boundary is maximally old. I think that's how it should behave. So please don't change it. A mask is a completely different function. You could perhaps add another slider (or a button that changes the behavior from a threshold to a mask) that would behave as you expect.

Note: If you could somehow flip around the values so that old and young ordering were reversed, you could also achieve your desired effect. Or, you could actually have another bright color on the bottom end of the scale and let the middle be dim. Then you'd move up the bottom slider to set a young threshold. But I like the first option better. So is there a way to create a new attribute that's a "reversal" of an existing one? You could put it in a new tool menu bar.