Migration to ember-data 1.0 beta7

As long as ember-data 1.0 brings many breaking changes, there's a lot of things to check...

- [ ] invoicesPending must be well sorted
- [ ] invoicesOverdue must be well sorted
- [ ] invoicesPaid must be well sorted
- [ ] quotationsPending must be well sorted
- [ ] quotationsFailed must be well sorted
- [ ] quotationsSucceeded must be well sorted
- [ ] purchaseOrdersPending must be well sorted
- [ ] purchaseOrdersSucceeded must be well sorted
- [ ] items must be well sorted