Support multi-dataset PieChart and align SectorChart layout

PieChart and PieChart3D now accept a list of sublists and render one
concentric ring per dataset (innermost first), so selecting them in a
Manipulate that feeds a matrix no longer produced a blank cell. Every
ring has the same thickness with a small gap between adjacent rings,
and each ring restarts the color cycle so rings are distinguished by
position rather than hue. SectorChart now sorts slices smallest-to-
largest and starts at the negative x-axis, matching PieChart's long-
standing convention.

Author: ad-si