Provide configuration to toggle child nodes pessimistically

[imkevinjones]

Say there is a checkbox tree such as this:

Only one child node is checked. By clicking the parent node, the remaining child nodes become checked.

If I want the default behaviour to pessimistically toggle the child nodes, it would be nice to have an optional prop to provide such configuration to the root checkbox tree.

With such a configuration option set, if I have two out of three child nodes checked, and I click the parent node, it should deselect all child nodes of that parent node. This would provide the opposite effect of the current optimistic toggling of child nodes.