Add graphical user interfaces for volumes, surfaces, higher-order structure

[Tom Goddard]

There are many Chimera graphical user interfaces that should probably be implemented in ChimeraX.
This ticket focuses on ones for volume data, surfaces and higher-order structure (Tools menu entries in those categories).

Here are the GUI interfaces not implemented in ChimeraX that are in those Chimera 1.15 menus.

Surface Color - radial/cylinder/height coloring, coloring by value or norm
Morph Map
Volume Filter - Gaussian, Median, Bin, Laplacian, Fourier, Scale, Flatten
Measure Volume and Area - implemented.
Volume Mean, SD, RMS - implemented.
Values at Atom Positions
Volume Series
Volume Tracer - partially implemented, missing Surfaces, Smooth, Transfer markers, Notes, ...

Surface Capping - subdivision, color, clip offset, disable

Unit Cell
Crystal Contacts - shows contacting subunits
Scale Bar
Icosahedron Surface
Small Angle X-ray profile - computed with Dina Schneidman FoXS web service
Flatten icosahedron - for making printed virus capsid models
Multiscale Models

[Tom Goddard]

I added the Map Mean, SD, RMS menu entry and corresponding volume statistics command.

[Tom Goddard]

Added measure volume and area tool.