Deprecates project, now just loads ember-data itself as add-on

This is prolly a WIP cause I haven't nested add-ons before so I'm not sure if this was the *right* way.

Note that right now `package.json` is referring to the git url directly since ember-data isn't published in npm yet. (so you can test this PR). Will `push -f` with a semver once it is.

Cc/ @rwjblue