Create "SAM: What is a Chemical Reaction?" interactive

[#59258328]
Update interactive groups.yaml, add "SAM: Chemical Reactions" group
Update "SAM: What is a Chemical Reaction?" interactive

[#59258328]

Add buttons, bar graph, update "About" text.
Fix temperature calculation when there are no atoms in the model

[#60065162]

Just return 0.
Add "SAM: Concentration and Reaction Rate" interactive

[#59258328]
Add "SAM: Temperature and Reaction Rate" interactive

[#59258328]
Add "SAM: Stoichiometry and Balancing Equations" interactive

[#59258328]
Convert chemical reaction parameters in "What is a Chemical Reaction?"

[#56871728]

Obviously that was the reason of the bigger vibrations, as default
dissociation energy was much higher than in Classic MW. The question
is whether it solves the problem completely.
Provide SVG image mapping in "What is a Chemical Reaction?"

[#59258328]
Provide SVG image mapping in "Concentration and Reaction Rate?"

[#59258328]
Provide SVG image mapping in "Temperature and Reaction Rate?"

[#59258328]
Fix "Temperature and Reaction Rate?" filename

[#59258328]
Use Arial font in images used by Chemical Reactions interactives

[#59258328]

Lato wasn't working e.g. on iPad. Arial is simple and should be
similar enough.
WIP on introducing-light-and-photons interactive

[#59258268]
Add legacy SAM "Excited States and Photons" CMLs

[#59258268]
Draft "Excited States and Photons" interactives

[#56363566]

Bootstrapped from the the conversion-test "quantum-collision" and "quantum-emission" examples.

Also, this includes a custom model for Excited States and Photons page 3. The MML converter didn't include a light sources section in the automatically-converted model. (is this correct or not?) However, the quantum dynamics converter expects a light source property with an 'on' method.
"Concentration and Reaction Rate": disable buttons when the model is played

[#59258328]
Reduce time step in "Stoichiometry and Balancing Equations" models

[#59258328]
"Temperature and Reaction Rate": disable slider when the model is played

[#59258328]
Chemical Reactions: let authors modify dissociation energy

[#59675484]