eagerInject/eagerEject should default to definition's options

I want to be able to define `eagerInject`/`eagerEject` on the resource deinition:

``` js
Article = DS.defineResource({
    name: 'article',
    eagerInject: true,
    eagerEject: true
})
```

Currently the create/destroy methods take the option only from the caller `Article.destroy(id, { eagerEject: true })`
