Update ember data guides to use @ember-data packages

[bmac]

No description provided.

[jenweber]

Thank you so much @bmac!

Notes to maintainers - the gameplan here is that for 3.11, we cut a release of the Guides, and then merge this in immediately so it shows up for 3.11 users but not 3.10. I added a label and an issue to help remind us #825

[locks]

@jenweber we can do both in this PR because we need a commit creating the 3.10 folder, right?

[locks]

Rebased to resolve conflicts.

[jenweber]

We can update, re-review, and merge, when the generators match the style of this PR. The generators currently produce:

import DS from 'ember-data';
const { Model } = DS;

export default Model.extend({

});

I'm marking this PR as WIP. Please let us know when we should take another look!

[jamescdavis]

The blueprints were updated to use package imports in emberjs/data#6358, which was released in [email protected]