Add `propTypes` to component definitions

[turnerhayes]

Prop types are a handy way of both adding run-time type validation and providing some documentation on the available props in the code. I believe that React disables prop type checking in production environments, so it shouldn't add any (or much) overhead in production.

[dylanesque]

If people are on board with this, I'd like to do at least a few of these, they're not especially difficult, but I want some practice implementing them.

[knod]

Remember to add these new ones as discussion items in the thread when the Alert System posts it so they don't get left behind!