[CHEC-1008] Feature/auth login handler

[jaepass]

• Added handler to exchange url token for jwt when user navigates back to site with email magic link
• Added login loading animation
• Manage customer data in Redux with action to set customer -> dispatch action from App.js on client side
• Edited App to use compose HOC and use setCustomer action from Redux store with connect

[linear[bot]]

CHEC-1008 Build login handler to handle email login links

When the user enters their email to log in, they will get an email sent to them. This email will contain a link back to the demo store URL. This page will need to accept a request which contains a token in the URL, and will need to make a request to Chec to exchange the token for a JWT: ``` POST /v1/customers/exchange-token token={token_from_url} ``` This API returns a JSON web token which authorizes the customer for 24 hours. Ideally we also do an API call to fetch the user's data ( `GET /v1/customers/{customer_id}` ) at this point, and we can store that locally too. After login, we can redirect the user to their "customer home" page which is built in another task.

[jaepass]

thanks for your help guys!