Move initializers into packages

This is a start for exposing the container initialization of Ember-Data. Having stand-along container initialization will allow us to use Ember-Data with `moduleForModel` in ember-qunit, and finally use real adapters instead of being limited to fixture adapter.

This first pass is very naive, but I'd like some feedback on an API before I go any further. I propose:

``` JavaScript
var container = isolatedContainer(); // as from EAK or ember-qunit
DS.setupContainer(container);
```

This implies a few other changes:
* [ ] Ember-Data uses a *single* initializer, which just calls `DS.setupContainer(container, application);`. The existing four-initializer setup goes away.
* [ ] `initializers.js` -> `ember_initializer.js`
* [ ] `setup_container.js` is used by `ember_initializers.js`. `setup_container.js` imports then uses the four functions created below (in order, `initializeDataAdapter`, `initializeTransforms`, `initializeStoreInjections`, `initializeStore`).
* [ ] `setupContainer` is imported and added to the `DS` namespace in `main.js`

/cc @rjackson @cavneb @abuiles