Improvements to package.json

Hi @wfwalker 

I found some time to poke around your project.  This PR includes some minor cleanup of the package.json file.

* You don't need to specify NodeJS Core modules in your package.json (I removed url, http, system)
* I added a repository URL to get rid of the npm warning
* I locked down your package dependencies. The wildcard '*' marker means that each time you run ```npm install``` you will download the latest version of each package, which might include breaking API changes.  A helpful tip: use ```npm install --save <package>``` to automatically update your package.json. (```--save-dev``` for development dependencies)
* Finally, I added a 'scripts' section including a 'start' command. This allows you to just type ```npm start``` from the top-level directory to start the server.