Split API implementations into apps.
Add ChildModelViewSetMixin to provide generic child list method.
Update requirements.txt for drf-toolbox, and update django to 1.6.2.
Add nested API for stores/categories and categories/items.
Add InvoicePermission.
Add api-auth url.
Apply InvoicePermission to InvoiceViewSet
Add permission checking for order API.
Remove Coupon API
Clean up serializers.
Add DeliveryWindowPermission
Add nested routing for invoices/orders.
Add OrderItem API.
Fix import errors.
Improve ChildModelViewSetMixin to handle complex model name.
Remove nested order_items.
Add delivery_buckets/orders API.
Add API doc.
Add Permission for DeliveryBucket API.
Add DeliveryBuckets permission detail.