Add natural key support to the document parsing app.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/document_parsing/managers.py

@@ -4,6 +4,7 @@ import logging
 import sys
 import traceback
 
+from django.apps import apps
 from django.conf import settings
 from django.db import models
 
@@ -48,3 +49,16 @@ class DocumentPageContentManager(models.Manager):
                 action_object=document_version.document,
                 target=document_version
             )
+
+
+class DocumentTypeSettingsManager(models.Manager):
+    def get_by_natural_key(self, document_type_natural_key):
+        DocumentType = apps.get_model(
+            app_label='documents', model_name='DocumentType'
+        )
+        try:
+            document_type = DocumentType.objects.get_by_natural_key(document_type_natural_key)
+        except DocumentType.DoesNotExist:
+            raise self.model.DoesNotExist
+
+        return self.get(document_type__pk=document_type.pk)