Rewrite using Rails middleware

[jorgemanrubia]

Instead of patching ‘render’, the engine now configures a rack middleware to analyze requests and modify responses.

This is much more robust since it is now independent of how the render method is invoked (or if it's invoked at all).

This will handle errors consistently now in both development and production mode. For development mode, I still had to patch ActionDispatch::DebugExceptions to discriminate remote requests we want to handle with turbolinks.

• Fix Handling 500s #1. Big kudos to @excid3 for his help on this one. In particular, his approach of using document.open/write/close fixed Returned <script> tags are not executed #4 as a very nice side effect 🙏😬.

• Fix Returned <script> tags are not executed #4

UPDATE: it's performing a full html replace now. See #7. Fixed in #8

Pending

• Test that <script> in responses are executed
• Add rails 6 test