Add 'isPropertyWritable' method to PropertySupport mixin

[#62719204]
Retain all properties (except outputs) that are bound to some widgets

[#62719204]
Update "onLoad" script in "Quantum Collision" interactive

[#62719204]

It ensures that textbox is always correct, even when related parameter
is retained during reload.
Let authors decide if property bound to component should be retained

[#62719204]

... during model reload / reset.
Use property binding in "Intermolecular Attractions and States of Matter"

[#62719204]
Fix "Diffusion & Molecular Mass", do not set params in "onLoad"

[#62719204]
Update "Pendulum" interactive

[#62719204]

Remove 'parametersToRetain' list from reloadModel call (these
parameters are retained by widgets anyway).
Remove 'reset' button which is now unnecessary.
Update "Spring" interactive

[#62719204]

Remove 'parametersToRetain' list from reloadModel call (these
parameters are retained by widgets anyway).
Remove 'reset' button which is now unnecessary.
Update "onClick Demo", use property binding instead of action scripts

[#62719204]
Update "Gravitational Fields (property-pulldown)" interactive

[#62719204]
Fix "One Radial Bond" interactive

[#62719204]
Merge pull request #60 from concord-consortium/widgets-retained-props

Properties that are bound to widgets are automatically retained