AJAX response data reporting

This update to raygun.js pushes AJAX response data into the error report to provide more context for an AJAX failure. In such an example, I can look at an error report with the following and know I don't need to do further investigation.

```
requestData	FirstName=Me&MiddleName=&LastName=Here&Gender=male&Dob=4+September%2C+2016&Email=here%40there.com&Phone=123456789
responseData	{"message":"The request is invalid.","modelState":{"model.Dob":["Date of birth must be in the past."]}}
```