Transition to functional React components

[emlys]

When we began developing the workbench, class components were the standard and functional components were new. React has moved away from class components, and functional components are the standard. I haven't seen any indication that class components will be deprecated any time soon, but there are some reasons it would make sense to convert our code to use functional components:

• Documentation about class components has been moved to a legacy site and is no longer updated
• It's increasingly hard to find tutorials and code examples using class components
• i18next is easier to use with functional components; exported class components require a workaround
• We often use the pattern of passing component functions as props to other components. eslint warns against this, and the recommended solution uses the functional component style.
• We have written our newer components using the functional style, and found it to work well and require less boilerplate code
• When working on code that uses both styles of components, I find it confusing having to switch back and forth

[R-Stev]

I should be able to adjust the class components.