[1.x] Correct middleware handling

[kapi2289]

There are still some things to be done before we can publish v1. I can see that InertiaCore lacks some of the functionalities from the official inertiajs/inertia-laravel repo.

• Determining the current version (Middleware.php)
• Applying the current version in the middleware (Middleware.php)
• Proper handling of default bag and X-Inertia-Error-Bag header (Middleware.php)
• Handling an empty response (Middleware.php)

These are changes to be made after merging #19. I would appreciate any help with this, as well as finding out other missing functionalities in this library.