Update Node to 6.13.0 LTS + current lib versions

[dbtlr]

This PR does the following:

• Updates recommendation for Node to the 6.x LTS: 6.13.0
• Updates all dependencies to their newest versions
• Swaps Jade for Pug, which is the newer library
• Basic code updates to update syntax for Express v4
• Adds Express libraries that were split off from core that now must be included explicitly
• Removes the /stats page
• Removes basic auth (as that was basically protecting the stats page)
• Removes Socket.io functionality, as we don't need real-time stats anymore

How to test:

• Install and use Node 6.13.0 (nvm makes this easy)
• Run npm install
• Run npm start
• Visit http://localhost:3000 -> you should see a simple HTML page
• Run curl -X POST -d "url=https://www.learnboost.com" localhost:3000 from another terminal
• This will return a url like: https://lrn.cc/0 You should be able to visit http://localhost:3000/0 to verify your redirect worked.

[dbtlr]

I updated this to use 6.13.0 and it works perfectly.

I updated the title and description to reflect this.