Add QA credits

[zepumph]

similar to phetsims/resistance-in-a-wire#89, there are no qa credits for the current sim in master. We should add them.

[zepumph]

@phet-steele let me know if the above commit looks good.

[phet-steele]

@zepumph it's good, but we need more now. Alex Dornan, Ethan Johnsonas well, please. You'll probably have to put a line break in there somewhere. Isn't this technically #54?

[zepumph]

Oh you're right thanks!

BTW here is what credits look like, they use MultilineText so you don't have to add new lines:

   if ( credits.qualityAssurance ) {
      children.push( new MultiLineText( StringUtils.format( creditsQualityAssuranceString, '\u202a' + credits.qualityAssurance + '\u202c' ), multiLineTextOptions ) );
    }

to be carried on in #54