fix django deprecation warnings

admin_interface/__init__.py

@@ -1,3 +0,0 @@
-# -*- coding: utf-8 -*-
-
-default_app_config = 'admin_interface.apps.AdminInterfaceConfig'

admin_interface/admin.py

@@ -3,7 +3,7 @@
 from admin_interface.models import Theme
 
 from django.contrib import admin
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 
 
 class ThemeAdmin(admin.ModelAdmin):

admin_interface/apps.py

@@ -2,7 +2,7 @@
 
 from django.apps import AppConfig
 from django.db.models.signals import post_migrate
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 
 
 class AdminInterfaceConfig(AppConfig):

admin_interface/models.py

@@ -8,8 +8,8 @@ from colorfield.fields import ColorField
 
 from django.db import models
 from django.db.models.signals import post_delete, post_save, pre_save
-from django.utils.encoding import force_text
+from django.utils.encoding import force_str
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 
 from six import python_2_unicode_compatible
 
@@ -301,7 +301,7 @@ class Theme(models.Model):
         verbose_name_plural = _('Themes')
 
     def __str__(self):
-        return force_text(self.name)
+        return force_str(self.name)
 
 
 post_delete.connect(Theme.post_delete_handler, sender=Theme)