Visualizing properties of mappings

There are many characteristics of mappings that may benefit from visualization. Multiple may be active at the same time. Ideally we can work out graphical symbolization of each property.

- [ ] is at default on horizontal axis
- [ ] is at default on vertical axis
- [ ] is non-default on 1 or more non-visible axes
- [ ] is a pin
- [ ] is selected

_This is an expanded version of #15._