Add prop-types, prop-type definitions

[CaitW]

prop-types

• We do not currently have a method for type-checking component props.
• Prop-types would be easy to add on a component-by-component basis as development continues
• We can omit the prop-types library from the production build, meaning little effective file-size increase

[theduckylittle]

I'm cool with keeping this alive a a potential enhancement and am generally a fan of type checking but in terms of dev effort, writing more tests will likely bear more fruit in the near term.