Notification on new orders (#3145)

* Trigger a notification when a new SalesOrder is created

- Notify the "responsible" owners (excluding the creator)
- Add unit test for new notification

* Adds notification when a new PurchaseOrder is created

* Add notification when a new build order is created

- Includes unit tests

* Refactor order notification code

- Adds a "exclude users" option for sending notifications

* Fixes for notification refactoring

* make notification a helper

* reduce statements togehter

* make reuse easier

* Add docs

* Make context variables clearer

* fix assertation

* Fix set notation

Co-authored-by: Matthias <code@mjmair.com>

InvenTree/templates/email/new_order_assigned.html

@@ -0,0 +1,11 @@
+{% extends "email/email.html" %}
+
+{% load i18n %}
+{% load inventree_extras %}
+
+{% block title %}
+{{ message }}
+{% if link %}
+<p>{% trans "Click on the following link to view this order" %}: <a href="{{ link }}">{{ link }}</a></p>
+{% endif %}
+{% endblock title %}