Added customer_nr to database and invoice templates.

Used standard DATEV format(10000 – 69999)

Fixes #31

resources/js/types/index.d.ts

@@ -92,6 +92,7 @@ export interface Customer {
     id: number;
     type: string;
     companyName: string | null;
+    customerNr: number | null;
     vatId: string | null;
     contacts: Contact[];
     email?: string;