Update metadata of several model properties

[arouinfar]

For #76

Lots of model properties need some combination of phetioDocumentation and/or units.

density.*Screen.model.gravityProperty

• add phetioDocumentation
• add units

density.*Screen.model.invisibleBarrierBoundsProperty

• add phetioDocumentation
• change to phetioReadOnly: true

density.*Screen.model.liquidMaterialProperty

• add units to density and viscosity values

density.*Screen.model.liquidViscosityProperty

• add units

density.introScreen.model.showMassesProperty

• add phetioDocumentation: Displays a mass readout on each block

density.*Screen.model.densityProperty

• add units

density.Screen.model.massProperty

• add units

density.introScreen.model.pool.liquidYInterpolatedProperty

• add phetioDocumentation

density.*Screen.model.pool.liquidVolumeProperty

• add phetioDocumentation

• add units

• For each block, buoyancyForceInterpolatedProperty, contactForceInterpolatedProperty, gravityForceInterpolatedProperty, massProperty, materialProperty (density/viscosity), and volumeProperty should have units.

• For each block, buoyancyForceInterpolatedProperty, contactForceInterpolatedProperty, gravityForceInterpolatedProperty should be phetioHighFrequency: true

• All instances of inputEnabledProperty should have this phetioDocumenation: Sets whether the element will have input enabled, and hence be interactive.

[jonathanolson]

add phetioDocumentation: Displays a mass readout on each block

This will be a bit weird for phrasing in Buoyancy. Do we need to switch the documentation for things between the sims?

[arouinfar]

This will be a bit weird for phrasing in Buoyancy. Do we need to switch the documentation for things between the sims?

Do you have any ideas for something that could work for both sims? It's preferable to keep the documentation the same, if possible.

[jonathanolson]

Implemented changes, can you verify?

Do you have any ideas for something that could work for both sims? It's preferable to keep the documentation the same, if possible.

I've used the word "mass" instead of "block", however that could be somewhat confusing with that phrase.

[kathy-phet]

What about the phrase "object" or "shape" instead of "mass". I do think "Displays a mass readout on each mass" will be hard to understand.

[jonathanolson]

Updated to "Displays a mass readout on each object" above.

[arouinfar]

@jonathanolson I missed the scale in my first review. Please make all of the following phetioReadOnly: true:

• density.mysteryScreen.model.scale.inputEnabledProperty
• density.mysteryScreen.model.scale.materialProperty
• density.mysteryScreen.model.scale.scaleForceInterpolatedProperty (also needs units of N)

[jonathanolson]

Implemented above, can you verify?

[arouinfar]

Looks good, closing.