Prevent order duplication

[KwikKill]

When the front is lagging or if the client double click, the post order is sent twice. We can prevent the order duplication by looking at :

• The user field
• The pizza in the order
• The payment method
• The payment type Raise error when the new order has the same value as the other

Later, this will be handled in the front too, asking if the user want :

• To merge the 2 orders
• To change the name and add it
• To cancel