WIP, Feature: Add the ability to add plugin scripts

[twilson63]

By enabling authors to add plugin scripts to incorporate new functionality into the application, it will provide more flexibility to the kit. For example, if you want to add auth0 to your application, it should be as simple as adding a pointer to a plugin script in your package.json

package.json

...
"plugins": {
  "auth": "./auth-plugin.js"
}

auth-plugin.js