Fix deprecation warnings for Django 1.11 and Django 2.0.

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

mayan/apps/ocr/models.py

@@ -12,8 +12,8 @@ class DocumentTypeSettings(models.Model):
     Define for OCR for a specific document should behave
     """
     document_type = models.OneToOneField(
-        DocumentType, related_name='ocr_settings', unique=True,
-        verbose_name=_('Document type')
+        DocumentType, on_delete=models.CASCADE, related_name='ocr_settings',
+        unique=True, verbose_name=_('Document type')
     )
     auto_ocr = models.BooleanField(
         default=True,
@@ -28,7 +28,7 @@ class DocumentTypeSettings(models.Model):
 @python_2_unicode_compatible
 class DocumentVersionOCRError(models.Model):
     document_version = models.ForeignKey(
-        DocumentVersion, related_name='ocr_errors',
+        DocumentVersion, on_delete=models.CASCADE, related_name='ocr_errors',
         verbose_name=_('Document version')
     )
     datetime_submitted = models.DateTimeField(
@@ -51,7 +51,7 @@ class DocumentPageContent(models.Model):
     Model that describes a document page content
     """
     document_page = models.OneToOneField(
-        DocumentPage, related_name='ocr_content',
+        DocumentPage, on_delete=models.CASCADE, related_name='ocr_content',
         verbose_name=_('Document page')
     )
     content = models.TextField(blank=True, verbose_name=_('Content'))

mayan/apps/ocr/tests/test_api.py

@@ -3,7 +3,7 @@ from __future__ import unicode_literals
 import json
 
 from django.contrib.auth import get_user_model
-from django.core.urlresolvers import reverse
+from django.urls import reverse
 
 from rest_framework import status
 

mayan/apps/ocr/views.py

@@ -1,9 +1,9 @@
 from __future__ import absolute_import, unicode_literals
 
 from django.contrib import messages
-from django.core.urlresolvers import reverse
 from django.http import HttpResponseRedirect
 from django.shortcuts import get_object_or_404
+from django.urls import reverse
 from django.utils.translation import ugettext_lazy as _
 
 from acls.models import AccessControlList