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.

Morph Map
Volume Filter - Gaussian, Median, Bin, Laplacian, Fourier, Scale, Flatten
Values at Atom Positions
Volume Series
Volume Tracer - partially implemented, missing Surfaces, Smooth, Transfer markers, Notes, ...

Surface Capping - subdivision, color, clip offset, disable

Icosahedron Surface
Small Angle X-ray profile - computed with Dina Schneidman FoXS web service
Flatten icosahedron - for making printed virus capsid models
Multiscale Models

Progress

These GUIs have been implemented

Scale Bar
Surface Color - radial/cylinder/height coloring, coloring by value or norm
Crystal Contacts - shows contacting subunits
Unit Cell
Measure Volume and Area
Volume Statistics

[Tom Goddard]

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

[Tom Goddard]

Added measure volume and area tool.

[Tom Goddard]

Added unit cell tool, and implemented unitcell command.

[Tom Goddard]

Added crystal contacts command and gui.

[Tom Goddard]

Added surface color gui.

[Tom Goddard]

Added scalebar command and gui. #4883