Fix ember-data version

Currently, `package.json` is used for built ember-data version instead
of `VERSION` file or `VERSION_STRING_PLACEHOLDER ` string.
Merge pull request #1690 from tricknotes/fix-version

Fix ember-data version
Now ember-data is built by `grunt buildPackages`

`bundle` is no longer used.
Merge pull request #1691 from tricknotes/update-readme

Now ember-data is built by `grunt buildPackages`