Fix deprecation warnings for Django 1.11 and Django 2.0.

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

mayan/apps/linking/models.py

@@ -102,7 +102,8 @@ class ResolvedSmartLink(SmartLink):
 @python_2_unicode_compatible
 class SmartLinkCondition(models.Model):
     smart_link = models.ForeignKey(
-        SmartLink, related_name='conditions', verbose_name=_('Smart link')
+        SmartLink, on_delete=models.CASCADE, related_name='conditions',
+        verbose_name=_('Smart link')
     )
     inclusion = models.CharField(
         choices=INCLUSION_CHOICES, default=INCLUSION_AND,

mayan/apps/linking/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.literals import (

mayan/apps/linking/views.py

@@ -3,8 +3,8 @@ from __future__ import absolute_import, unicode_literals
 import logging
 
 from django.contrib import messages
-from django.core.urlresolvers import reverse, reverse_lazy
 from django.shortcuts import get_object_or_404
+from django.urls import reverse, reverse_lazy
 from django.utils.translation import ugettext_lazy as _
 
 from acls.models import AccessControlList