[ON HOLD] Enable passing through the requests to the original URL v2

[prantlf]

If passThrough is true, performs the request with the original settings and lets the onAfter[x] callback modify the response:

$.mockjax({
  url: '/api/currentuser',
  passThrough: true,
  onAfterSuccess: function (response) {
    response.image = '/images/profile';
  }
});

This suggest a resolution for the second half of the #225.

[jakerella]

@dcneiner Can you review this one as well?

@prantlf Same as the other PR, looks like some small conflicts crept in. Can you resolve?

[dcneiner]

@prantlf @jakerella Please see my comments on #232, as that will impact this PR some. I think this PR looks good, though I'd recommend renaming the function variable passThroughCallbacks to something that reflects its more generic usage. Perhaps wrapCallbacks or something you like better.

Thanks again for your work on this!

[jakerella]

On hold until conflicts can be resolved.

[jakerella]

Closing this PR for inactivity. The issue is still there, and the code is on a good path. Any new PR would need to be merged into master at this point.