Fixed and finalized implementation of logic for Register

Implemented Register component's form and submitForm() handler

Basic implementation of ProductDetail component; cleanups in others

CategoryDetail logic and pseudo-UI implemented! :)

Registered propTypes with CategoryList and CategoryDetail components

Implemented Linking to each Category in CategoryList

Fixed error with using resulting res.data object in CategoryList

Added 'proxy' to backend app URL in package.json

Imported relevant and needed API services into each component

Added API service objects to make CRUD calls against the backend RESTful API endpoints

Updated layout/Header component to Link to other routes

Added Routes for the store-section of the app

Setup initial routes for profile-section

Added placeholder text for store-related components

Setup 'instructional placeholders' for profile-related components