Enable JsonResponseHandler for Whoops! to send JSON formatted errors for AJAX requests

[GwendolenLynch]

An example of what is given in error generating AJAX requests now:

{
    "error" : {
        "type" : "UnexpectedBeerException",
        "message" : "Expected more beer in request. Unable to continue!",
        "file" : "src/Application.php",
        "line" : 123
    }
}

NOTE This attaches to the Whoops! service provider, so will only be sent in the cases where a HTML Whoops! otherwise would.

Changelog

• Whoops now sends errors to AJAX callers in JSON format

[GwendolenLynch]

Hold this... Might need to tweak.

[GwendolenLynch]

OK, good to go... Once Travis agrees!

[bobdenotter]

A'ight!