Link associated Nodes and checkboxes to the same visibleProperty

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3/4/21 design meeting change request, related to #137 and #139

For all Nodes whose visiblity is controlled via a checkbox, link them to the same Property that is controlled by the checkbox. For example, rootsNode, vertextNode, ...

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The only element that was capable of using a checkbox Property directly was graphingQuadratics.focusAndDirectrixScreen.view.pointOnParabolaManipulator.visibleProperty.

Visibility of other Nodes was derived from a checkbox Property and some other state. For example, vertextNode is only visible if the checkbox is checked and the curve has a vertex.

What I did discover is many instances of setting some visibleProperty to phetioReadOnly: true specified in overrides.js. I moved all of them to code. Here's why:

Anything that is derived in the code should be specified as phetioReadOnly: true in the code. That's the case for for these elements:

graphingQuadratics.focusAndDirectrixScreen.view.focusManipulator.visibleProperty
graphingQuadratics.focusAndDirectrixScreen.view.vertexManipulator.visibleProperty
graphingQuadratics.standardFormScreen.view.noRealRootsNode.visibleProperty
graphingQuadratics.standardFormScreen.view.rootsNode.visibleProperty
graphingQuadratics.standardFormScreen.view.vertexNode.visibleProperty
graphingQuadratics.vertexFormScreen.view.vertexManipulator.visibleProperty

phetioReadOnly: true was duplicated 4 times each for these buttons, which appear in all screens. It makes sense to move this to the code, so that one screen isn't accidently set differently.

equationAccordionBox.buttonGroup.eraseButton.visibleProperty
equationAccordionBox.buttonGroup.saveButton.visibleProperty

So... @amanda-phet please review. Here's what you need to verify:

• *.pointOnParabolaManipulator.visibleProperty is linked to *.viewProperties.pointOnParabolaVisibleProperty
• All of the elements enumerated above are read-only

[amanda-phet]

Verified the above.

I am a little confused- First, did @kathy-phet and I set these to as phetioReadOnly: true in overrides.js? I don't remember that, nor did I realize we could do that. I thought we could only specify the featured items in that file.

Second, are these ReadOnly because they can be set by the client within the sim by just checking the box? I can't remember why we'd want these to be ReadOnly.

[amanda-phet]

It appears my questions are answered in #149 .