Add screen-specific screenshots to sim checklist

[arouinfar]

See https://github.com/phetsims/website/issues/1322

In addition to alternate screenshots that show up on the sim page, we should also be taking screen-specific screenshots for the metadata service. Alt and screen-specific screenshots may be redundant but aren't necessarily.

Self-assigning to update the sim checklist.

[arouinfar]

Sim checklists to update:

• geometric-optics
• geometric-optics-basics
• greenhouse-effect
• buoyancy
• my-solar-system
• number-play
• center-and-spread
• eating-exercise-and-energy
• calculus-grapher
• build-a-nucleus
• normal-modes
• x-ray-diffraction

[arouinfar]

Done, except for calculus-grapher which I noted in phetsims/calculus-grapher#1.

[arouinfar]

The instructions I added to the sim checklist were too vague. Screen-specific screenshots should be taken with the screens query parameter. Re-opening to update the checklist template and checklists for sims in active development.

• template checklist
• build-a-nucleus
• buoyancy
• calculus-grapher
• center-and-variability
• eating-exercise-and-energy
• greenhouse-effect
• mean-share-and-balance
• models-of-the-hydrogen-atom
• my-solar-system
• normal-modes
• number-compare
• number-play
• sound
• quadrilateral
• x-ray diffraction