Add concatenation to built version

[korzio]

As a "frontend" djv user I want to
My built djv package uses a single anonymous function

module.exports = {  
  plugins: [
    new webpack.optimize.ModuleConcatenationPlugin()
  ]
};

• Update to webpack 3
• Add a ModuleConcatenationPlugin
• Add a npm prepublish hook to built everything before a package is actually published
• Add sourceMaps for an uglified version

[korzio]

#39