Refactorings/eager loading

This pull request refactors the way eager loading is transformed into sql queries. Where we previously had been searching for a model that matches the passed string, we now just pass the model and probably specify the alias which is used in the association:

```js
Model.find({ include: [ AnotherModel ] })
Model.find({ include: [ { daoFactory: AnotherModel, as: 'associatedAlias' } ] })
Model.find({ include: [ {model: AnotherModel, as: 'associatedAlias' }]
```