QD: Special-case cardinal directions for light-beam

Using old method, selecting 5 beams from South would place them
1/5th of the model apart, so 5th beam would be at very far edge of
model. This keeps all 5 beams 1/6th of the model apart.

This special-casing of the 4 cardinal directions is analogous to
the Class MW method,
https://github.com/concord-consortium/mw/blob/d3f621ba87825888737257a6cb9ac9e4e4f63f77/src/org/concord/mw2d/models/AtomicModel.java#L2514

[#59509106]
QD: Make proportion of interactable CO2 element-type higher

Previously half of CO2 atoms were actually an non-interactable element.
This decreases the proportion of those.

[#59509270]
QD: Create slow-motion checkbox for Sun On Ground interactive

[#59508924]