Add missing unicode literals usage

Fixes rb#580
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/models/dictionary.py

@@ -18,6 +18,8 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
+from __future__ import unicode_literals
+
 import sys
 
 from django.core.urlresolvers import reverse

weblate/trans/models/project.py

@@ -18,6 +18,8 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
+from __future__ import unicode_literals
+
 import os
 import os.path
 

weblate/trans/models/translation.py

@@ -18,6 +18,8 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
+from __future__ import unicode_literals
+
 import os
 import codecs
 from datetime import timedelta

weblate/trans/models/unit.py

@@ -18,6 +18,8 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
+from __future__ import unicode_literals
+
 import functools
 import traceback
 import multiprocessing

weblate/trans/models/unitdata.py

@@ -19,6 +19,7 @@
 #
 
 from __future__ import unicode_literals
+
 from django.db import models
 from django.db.models import Count
 from django.contrib.auth.models import User