(Design) Purchase Orders

[jniles]

This issue proposes the database schema for purchase orders in 2.x

Schema
The purchase table has a lot information unrelated to the actual purchase order to be sent to the supplier. We should start small with only the necessary information and try to add in more if we need it.

column	type	description
uuid	BINARY
project_id	INT
reference	INT	A generated ID that, combined with project_id, creates a human readable id
cost	DECIMAL	the total cost of the purchase order
date	DATETIME	the date of the purchase order
currency_id	INT	the id of the currency the order is made in
note	TEXT	some text describing the nature of the purchase order
creditor_uuid	BINARY	the creditor to be sent the purchase order
created_at	TIMESTAMP	set at the server time when the record was created

The table purchase_item doesn't need to change.

For the first iteration, this will be all the properties stored in the purchase order table.

HTTP API
The HTTP API will follow the standard API Guidelines. You will not be able to delete a Purchase Order yet, until that case is analyzed.