Refactor relationships with links

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Fixes http://discuss.emberjs.com/t/requests-triggering-multiple-times/6316
sure :+1:  I'm reading over every new PR against this repo, we make heavy use of ED, but one of our API's is so un-conventional that we have such crazy [serializer](https://gist.github.com/intuitivepixel/0b6a10cc70a3a42f0f66) to bring the JSON payload in shape before ED get's it ...