added newsletter with functionality and server

[gmnikhil]

Added newsletter UI and functionality.

closes: #11

When email is submitted, a document containing field email is added to firebase collection named 'newsletters'.

When newsletter is published, an email is sent to all the various emails in the 'newsletter' collection.

Server is set up using node.js.

Info to start server:

This server runs at port 3000.

Make sure you start server first before starting client.

Steps to Follow to correctly start Server:

• run npm install in server directory
• get service account admin credentials for Node.js from firebase (for this you need to go and create a firebase project)
• save the credentials in secrets folder as a file named serviceKey.json
• update cred.js file in secrets folder with your own email and password. Email will be sent via this account.
• run npm start in server directory

What does server do?

• Adds email to a collection named newsletters.
• Sends email to everyone in collection when a newsletter is published

I have written the above in a README in the server folder for future reference.

BASE_URL can be changed in the constant.js in src/constants

I am a DWOC participant.

Do assign me points.

Thanks for assigning this to me.

[gmnikhil]

@Priyanshu-official @JoshuaPoddoku