PhET-iO change requests (Two Atoms screen)

[pixelzoom]

Related to #85... Change requests for PhET-iO instrumentation:

Uninstrument these elements:

• [x] platesNode
• [x] partialCharge*Node
• [x] bondDipole*Node
• [x] molecularDipoleNode
• [x] arrow*Node, the individual hint arrows
• [x] electrostaticPotentialColorKey
• [x] electronDensityColorKey

Add these query parameters:

• [x] dipoleDirection, values 'positiveToNegative' and 'negativeToPositive', add to spreadsheet
• [x] surfaceColor, values 'RWB' and 'ROYGB', add to spreadsheet

Studio tree structure:

• [x] Put color key elements under a common parent, view.colorKeysNode.visibleProperty
• [x] Fix tree structure for electronegativityPanels, all panels under electronegativityPanels
• [x] Put all "Three Atoms" listeners under moleculeNode.dragListeners
• [x] Put all hint arrows under moleculeNode.hintArrowsNode
• [x] Rename Atom.name to Atom.label, AtomNode.nameText to AtomNode.labelText
• [x] Get rid of EField class, pull eFieldEnabledProperty up into model.

Documentation (phetioDocumentation):

• [x] angleProperty: indicate which direction is positive
• [x] positionProperty: relative to the view coordinate frame, (0,0) at upper-left of layoutBounds, +x right, +y down.
• [x] partialChargeProperty: "qualitative scalar representation of partial charge, computed as the electronegativity difference"
• [x] bond.dipoleProperty: "qualitative vector representation of dipole, based on the electronegativity difference"
• [x] molecule.dipoleProperty: 'the molecular dipole, vector sum of the bond dipoles'
• [x] surfaceColorProperty: indicate that it applies to the Real Molecules screen

[pixelzoom]

I moved a couple of change requests to #91, because they are going to require significant effort.

@arouinfar The requests in the list above are done, and ready for review in master.

[pixelzoom]

@arouinfar pointed out that I used 'RGB' instead of 'RWB' for one of the ?surfaceColor values. Fixed in the above commit.

[arouinfar]

@pixelzoom everything is looking good in master. I'll leave this issue open and self-assigned since we still need to review the Three Atoms screen in detail.

[pixelzoom]

@arouinfar since these change requests were for the "Two Atoms" screen, I've retitled this issue to "PhET-iO change requests (Two Atoms screen)", and I'm going to close this issue.

85 (Add basic PhET-iO instrumentation) is still open, assigned to you and @kathy-phet, and that's the appropriate place to continue your review of the "Three Atoms" screen . If you have change requests for that screen, create another issue like this one. Thanks!