Add GraphQL API

[ahoopes16]

Summary

In order to save our guests' responses when they RSVP to the wedding, we need to have a database set up. AWS Amplify automatically sets this up for you when you add and API component to your application, so I decided to add a GraphQL API to the application.

I also had to define the GraphQL schema, which I based off of the following model.

This PR closes #35, and unblocks #36 and #37.

How to Test

Testing for this would be very difficult - you'd have to create an AWS Console Account, pull this repo down, register your own cloud account using the Amplify console, etc.

Since I'm developing this alone, I'm not going to spend the time to explain the whole process, but please look in the Suggested Reading section below for useful videos/documentation!

Suggested Reading

• Complete Coding - Creating an AWS Amplify Application
• Complete Coding - Working with Data in DynamoDB from React in AWS Amplify
• AWS Amplify Documentation for Deploying a Serverless Full Stack Application

[ahoopes16]

I had to do a lot of work to get that build to pass, but it finally did... Not sure why I can't get that check to go green now, but it is working properly inside AWS :)