Document conventions for credits.

[pixelzoom]

In phetsims/natural-selection#270 (comment), I was asked to revise the "Lead Design" credits in Natural Selection because the convention had changed. I tried applying this to other sims, but the ordering needed clarifiction. So @kathy-phet, @amanda-phet, @arouinfar, and I had a Slack discussion about conventions.

Consensus:

• leadDesign = Primary HTML5 designer first, followed by contributing designers (legacy & secondary HTML5) in alphabetical order
• softwareDevelopment = Primary HTML5 developer first, followed by contributing developers (legacy & secondary HTML5) in alphabetical order
• team = HTML5 and legacy team members, in alphabetical order
• contributors, qualityAssurance, graphicArts, soundDesign = alphabetical order (these categories are new for HTML5, so no legacy considerations)

TODO:

• Update documentation in CreditsNode.js - @pixelzoom
• Review CreditsNode.js - @arouinfar
• Update checklists - @arouinfar

[pixelzoom]

Documentation in CreditsNode.js was updated in the above commit.

Over to @arouinfar for next tasks.

[arouinfar]

Thanks @pixelzoom! Everything looks good. I added a link to CreditsNode.js to the master checklist template, see commit above.