Add a configurable, independent 'order material type' field to POL

Purpose:

User needs the ability to customize their list of material types specific to orders and order lines for accurate tracking and reporting on order activity. These material types will not be an accurate reflection of the variety of individual items that may be acquired via this purchase order.

In addition to having the separate list, RM SIG wants to be able to set a default item material type from the Orders perspective, so that when an Order is set to create an item record, they don’t have to set the material type at that point.

Use case:

• Use a default item material type of “On Order” or “Pending” to signal that the real item material type value had not yet been set. Libraries would not HAVE to do that if they don’t want to.
• Users need the separate Order Material Type to support their own reporting needs. In addition, they want to be able to have values that may be less or more granular than the item material type list would be, since it’s supporting different needs.

Requirements:

• Allow the user to add, edit and delete values from the list of "Order material types" in the Orders module settings
• You should not be able to remove a value that is in use by one or more orders
• Each purchase order line can be assigned 1 order material type
• Should Not be a required field
• Should always be editable
• Should be an alphanumeric value
• Change label of existing "Material type' field to "Item material type"