Create order_slip webservice

To use this new webservices, you have to access to api/order_slip/
"order_slip_detail" is a virtual entity inside "order_slip" webservice.
If you make a PUT request to this entity without association, all the order_slip_details will be lost, you have to pay attention.
Behavior of this entity is similar to "carts" entity.
For each PUT request you have to specify associations (order_slip details)
By typing this URL you can get more information about this entity :
api/order_slip/?schema=synopsis
This entity have been tested under 6 online shops.