Fix deprecation warnings for Django 1.11 and Django 2.0.

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

mayan/apps/metadata/models.py

@@ -151,9 +151,12 @@ class DocumentMetadata(models.Model):
     """
 
     document = models.ForeignKey(
-        Document, related_name='metadata', verbose_name=_('Document')
+        Document, on_delete=models.CASCADE, related_name='metadata',
+        verbose_name=_('Document')
+    )
+    metadata_type = models.ForeignKey(
+        MetadataType, on_delete=models.CASCADE, verbose_name=_('Type')
     )
-    metadata_type = models.ForeignKey(MetadataType, verbose_name=_('Type'))
     value = models.CharField(
         blank=True, db_index=True, max_length=255, null=True,
         verbose_name=_('Value')
@@ -200,11 +203,12 @@ class DocumentMetadata(models.Model):
 @python_2_unicode_compatible
 class DocumentTypeMetadataType(models.Model):
     document_type = models.ForeignKey(
-        DocumentType, related_name='metadata',
+        DocumentType, on_delete=models.CASCADE, related_name='metadata',
         verbose_name=_('Document type')
     )
     metadata_type = models.ForeignKey(
-        MetadataType, verbose_name=_('Metadata type')
+        MetadataType, on_delete=models.CASCADE,
+        verbose_name=_('Metadata type')
     )
     required = models.BooleanField(default=False, verbose_name=_('Required'))
 

mayan/apps/metadata/tests/test_api.py

@@ -1,8 +1,8 @@
 from __future__ import unicode_literals
 
 from django.contrib.auth import get_user_model
-from django.core.urlresolvers import reverse
 from django.test import override_settings
+from django.urls import reverse
 
 from documents.models import DocumentType
 from documents.tests import TEST_DOCUMENT_TYPE_LABEL, TEST_SMALL_DOCUMENT_PATH

mayan/apps/metadata/views.py

@@ -3,9 +3,9 @@ from __future__ import absolute_import, unicode_literals
 from django.conf import settings
 from django.contrib import messages
 from django.core.exceptions import ValidationError
-from django.core.urlresolvers import reverse, reverse_lazy
 from django.http import HttpResponseRedirect
 from django.shortcuts import get_object_or_404
+from django.urls import reverse, reverse_lazy
 from django.utils.encoding import force_text
 from django.utils.http import urlencode
 from django.utils.translation import ugettext_lazy as _, ungettext