implement useRef hook

[JRJurman]

Summary

React has a useRef hook which is useful for having a mutable value that persists across renders and doesn't trigger re-renders itself. We should add a similar hook for tram-one!

Potential Implementation

Similar to how the useState hook works, we should use the workingKey value to create uniquely namespaced keys. However we can create a direct mapping to the global space with this namespaced key (rather than creating a Hover Engine action group).

[JRJurman]

This ticket may become easier to understand after the diagrams for #128 is resolved. Any questions can be directed to me in the interim, either here or on our slack.

[JRJurman]

So, this can be potentially resolved by providing a ref in the useEffect hook. This would be really trivial to do, and can be added as a minor (non-breaking) change.

[JRJurman]

There are effects that depend acting on the element that is generated, and using useRef here could be a good way to "do these things anytime a rerender is triggered" - since those effects are dependent on the instance of the element that is rendered.