Suggested live demo improvements

[cstarkjp]

1. Change "Steps" to "Duration" and have this number reflect max time not max iterations, i.e., adjust by 1/2 for staggered D-K.
2. Implement $\mu_3$ = $N p_3$ rather than $p_0$ (just call it $\mu$?)
3. Implement "Presets" with 3 or more exemplary parameter group choices. — DONE
4. Fix slider button color, size?
5. Subscript $p_1$ etc
6. Maybe just have x, y, z, rather than $n_x$, $n_y$, $n_z$ — DONE
7. Possibly annotate sliders, canvas with range, axis values? Or perhaps not, for compactness. Or maybe just annotate with x, y or t, along canvas axes?
8. Implement an "auto" or "play" viz mode that spins through the slices automatically to provide an animation. This could be the default, which would make communication of the model and the tool more effective. — DONE
9. Possibly replace the zoom slider with a limited set of radio buttons: 1x, 2x, 3x, 5x. I have limited the range down from 10x to 5x because the slider doesn't work well on mobile for a large range (automatic page resizing and zoom out becomes unmanageable), which makes me think buttons would be easier. 2x could be the default. Remember that on laptops and on mobile there's zoom capability anyway that makes this widget less than essential.
10. Set Steps=500 for 2d default. — DONE