Handle and emit PSR-7 responses

[chrisvanpatten]

For greater consistency with other modern PHP frameworks, Kaiso should expect controllers to return PSR-7 response, and emit them to the server instead of relying on WordPress' mysterious implementation of response emitting.

Kaiso already makes a PSR-7 Request object available in controllers, and this would be a logical extension of that behaviour.

Some potential emitter libraries:

• https://github.com/zendframework/zend-httphandlerrunner
• https://github.com/narrowspark/http-emitter