Add MongoDB Atlas

[junerockwell]

This new version is a replacement of mLab by using MongoDB Atlas as the DBaaS, and has updates to the latest Mongoose.

Highlight Changes:

1. Now using async/await replacing long promises.
2. Now using MongoDB Atlas replacing mLab.
3. Now using restify-errors package.
4. Now using JSON Web Token!!!
5. Unlike the original samples, this one has more defined Signup/Login endpoints, and added a sample API endpoints for notes to demonstrate CRUD.
6. Unlike the original samples, this one uses dotenv. I committed the .env file for demonstration purposes but in real life, we should not commit it to Git.
7. Using restify-namespace since I decided to go the extra mile and make the Notes API to demonstrate CRUD.
8. Now using mongoose-timestamp plugin to take care of the createdAt and updatedAt timestamps automatically.
9. Now using bcryptjs instead of node-bcryptjs, and made it work with JWT.

What I learned:

1. How to use JSON Web Tokens.
2. How to navigate around MongoDB Atlas. It's very different from mLab, but it's a DBaaS nonetheless.