Added customer_nr to database and invoice templates.

Used standard DATEV format(10000 – 69999)

Fixes #31

database/factories/CustomerFactory.php

@@ -3,6 +3,7 @@
 namespace Database\Factories;
 use App\Models\PaymentTerms;
 use Illuminate\Database\Eloquent\Factories\Factory;
+use App\Http\Controllers\CustomerController;
 
 class CustomerFactory extends Factory
 {
@@ -13,6 +14,7 @@ public function definition()
         return [
             'type' => $this->faker->randomElement(['private', 'business']),
             'company_name' => $this->faker->company(),
+            'customer_nr' => CustomerController::generateCustomerNumber(),
             'vat_id' => $this->faker->numerify('DE##########'),
             'tax_id' => $this->faker->numerify('DE##########'),
             'global_id' => $this->faker->numerify('############'),