Add time-grunt

Shows elapsed time of tasks at the end.
Switch to load-grunt-tasks

https://github.com/sindresorhus/load-grunt-tasks
Remove ember-data revision number

Since Ember Data 0.13 the API revision check has been removed.
You no longer need to provide the API revision number when defining your
store, see http://emberjs.com/blog/2013/05/28/ember-data-0-13.htmlhttp://emberjs.com/blog/2013/05/28/ember-data-0-13.html#toc_api-revision-removal
Update dependencies
[Fixes #84] grunt build uses ember.prod and ember-data.prod