feat: add Modifiers + ModifierGroup Common Models

[paulkr]

Updates:

1. Added Modifiers and ModifierGroups Common Models.
2. Added Discounts model to Orders Common Model.
3. Added Taxes to Orders Common Model.
4. Added name, type, category, and jurisdiction to Taxes Common Model.
5. Renamed taxCode to code, taxRate to rate, taxAmount to amount in Taxes Common Model.
6. Added tax, discount, discountLines to Items Common Model.
7. Changed tax in Products Common Model to an array of Taxes.
8. Add parentId to Categories Common Model.