ZODB Components: erp5_trade: Migrate TestOrder{Mixin} and all Unit Tests inheriting from these classes.

Also, Split testInvoice to a Module Component in erp5_invoicing for Mixins used
by several other tests and Test Component in erp5_simplified_invoicing (initially
everything was migrated to erp5_invoicing but this does not work as Alarm_buildInvoice
is different in simplified and advanced invoicing).