Use AFMotion instead of Bubblewrap for HTTP

This request is because Bubblewrap is removing their HTTP module:
https://github.com/rubymotion/BubbleWrap/issues/308

I tried to change as little as possible, but "success" is returned by AFMotion instead of "ok" like Bubblewrap. So this is a breaking change. I could create a pull request on AFMotion to add an alias but "success" is actually more correct.

The specs are broken because Webstub does not support AFMotion. It's noted here:
https://github.com/mattgreen/webstub/issues/20
I tested with my app and the example app and I haven't found any issues. Not sure what to do about it.

It would be better to move to AFMotion's JSON parser and remove Bubblewrap entirely but that is a bigger change that I didn't want to tackle.