updated sample app ebextensions, updated syntax and conventions

[hacbrown]

Description of changes:

• The current application is broken because it relies on a .ebextensions that are built for AL1. This is updated to work with AL2
• The application has severely out of date code, I've modernized the syntax and updated the package-lock.json file. I've removed the old npm-shrinkwrap.json which locks in older package versions.
• I've updated the README.md to contain more up-to-date instructions that are consistent with what is described here. https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/nodejs-dynamodb-tutorial.html . This means we recommend customers add specific policies to the aws-elasticbeanstalk-ec2-role via the console, rather than adding policies via the iam_policy.json file. I've also changed the naming to nodejs-example-express-dynamo to be a more accurate description and differentiate it from our default sample app.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Testing

I've deployed an application via the README instructions and verified it worked.