Fix named-amd exports.

Ember does not export named-amd yet. We are shimming the `ember` module to have a single `default` export (this is exactly what EAK and ember-cli expect).

This means that using the following:

```javascript
import {get} from 'ember';
```

Which transpiles to:

```javascript
var get = __dependency1__.get;
```

Will not actually work since `__dependency1__` will only have a single property (`default`) and not a `get` property.

-----

This changes the imports to match reality. At some point, Ember will actually provide real ES6 (and possibly AMD) builds so I kept the variables that we were importing previously stashed at the top of each module (so that when we can do `import {get} from 'ember';` it is as simple as changing these same lines back).
The point when ember will expose its pieces as modules to be imported on demand is far in the future? What is holding it?

Just curious.