Quality accessible source code

[blairlyons]

• [ ] https://github.com/simularium/simularium-viewer/issues/150
• [ ] https://github.com/simularium/simularium-viewer/issues/159
• [ ] https://github.com/simularium/simularium-viewer/issues/224
• [ ] https://github.com/simularium/simularium-planning/issues/126
• [x] https://github.com/simularium/simulariumio/issues/78
• [ ] https://github.com/simularium/simularium-viewer/issues/141
• [ ] https://github.com/simularium/simularium-viewer/issues/134
• [x] https://github.com/simularium/simulariumio/issues/70

Publicly available, performant, modular, commented, well-organized source code.