added pdf template and other invoice improvements (#1693)

src/Entity/InvoiceTemplate.php

@@ -10,6 +10,7 @@
 namespace App\Entity;
 
 use Doctrine\ORM\Mapping as ORM;
+use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
 use Symfony\Component\Validator\Constraints as Assert;
 
 /**
@@ -19,6 +20,7 @@ use Symfony\Component\Validator\Constraints as Assert;
  *          @ORM\UniqueConstraint(columns={"name"})
  *      }
  * )
+ * @UniqueEntity("name")
  */
 class InvoiceTemplate
 {