Scoped generator install

[jho406]

Superglue’s generators feel a bit invasive. And by that I mean we install the helpers onto the ApplicationController which could affect things downstream for existing apps. In practice, I often find myself having a dedicated SuperglueController, and a superglue.json.props layout instead of the usual ApplicationController and application.json.props.

For this work, let’s generate a SuperglueController < ApplicationController and add all the code we normally add to ApplicationController to there. Other generated controllers should inherit from this controller. This would start the dev off to selectively control which pages should be in react and which pages should be in normal HTML.