[BUGFIX beta] {{view}} helper no longer uses Ember.View global, instead uses container view:default

During the ES6-ify process @rjackson left a comment mentioning that the `{{view}}` helper needs to not look up `Ember.View` globally. This PR fixes this by looking up `view:default` from the container (which `Ember.View` is registered at, by default).

Although I'd love to see this merged asap, it's possible some peoples are overriding `view:default` (we are) and this change from `Ember.View` *might* produce unexpected results. On the other hand, if you're like us, this has been very desirable since we provide our own `default` base classes that inherit from their core objects. This is why I didn't `FEATURE` flag this, but I'm more than happy to.

Also of note is that there was not previously a unit test for using `{{view}}` without providing a path, which this now includes. Some minor adjustments were needed to some other tests, mostly just injecting a container with a `view:default`.