Cannot use Ember beta / canary easily.

When choosing `canary` / `beta` / `release` as the Ember version for a newly created twiddle, an error is displayed. This started once https://github.com/ember-cli/ember-twiddle/pull/532 was deployed. The work around is to move `ember-data` out of `addons` and into `dependencies` (in the `twiddle.json`).

As of https://github.com/ember-cli/ember-twiddle/pull/532 `ember-data` is now consumed as an addon. This leverages the addon builder backend to build the addon for the specific Ember version. Unfortunately, the addon builder does not currently support building for the various Ember release channels.

I have taken a crack at working on that in https://github.com/joostdevries/twiddle-backend/pull/27, but really need @joostdevries' and @Gaurav0's advice there to ensure we aren't shooting ourselves in the foot.