Refactor relationships with links

Placeholder
Fixes http://discuss.emberjs.com/t/requests-triggering-multiple-times/6316
@igorT this is going to break the new `manyArray.reload` method? https://github.com/emberjs/data/blob/master/packages/ember-data/lib/system/relationships/relationship.js#L180 
I'm just asking because I use  `manyArray.reload` a lot.