Keypad should use nested options for its NumberAccumulator

[zepumph]

Discovered while working on #540. Tagging @Denz1994 to see what he thinks.

[zepumph]

Right now [in Keypad.js] I have to omit the parent tandem before passing in the child one:

    // @private {function}
    this.keyAccumulator = options.accumulator ? options.accumulator : new NumberAccumulator( merge( {
      tandem: options.tandem.createTandem( 'numberAccumulator' )
    }, _.omit( options, 'tandem' ) ) );

[pixelzoom]

I don't see any opportunities for using nested options in NumberAccumulator.

@zepumph Do you mean that KeyPad should use nested options for its NumberAccumulator subcomponent?

EDIT: I'm going with "yes".

[pixelzoom]

I'm going to work on this issue, self assigning.

[pixelzoom]

There are 5 occurrences of import Keypad from (in 4 repos) to be inspected for use of NumberAccumulator options:

• area-model-common
• collision-lab
• fourier-making-waves
• projectile-motion
• scenery-phet demo

The complete set of NumberAccumulator options (including AbstractKeyAccumulator superclass) is:

• additionalValidator
• maxDigits
• maxDigitsRightOfMantissa
• tandem

[pixelzoom]

Options accumulatorOptions was added to Keypad in the above commit, and adjustments were made to sims. area-model-common required no adjustments because it provides options.accumulator to Keypad, therefore making options.accumulatorOptions irrelevant.

In additon to testing all sims that use Keypad, I inspected the Studio tree in projectile-motion (screenshot below) and it looks correct.

@zepumph would you mind doing a quick review, since you created this issue?

[zepumph]

Looks really nice. Thanks