Index Proposal.datetime

It's used to sort Votes, takes votes list of 10 items in the API from 5s
to 300ms.

representatives_votes/migrations/0010_proposal_datetime_index.py

+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('representatives_votes', '0009_dossier_ext_link'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='proposal',
+            name='datetime',
+            field=models.DateTimeField(db_index=True),
+        ),
+    ]

representatives_votes/models.py

@@ -27,7 +27,7 @@ class Proposal(HashableModel, TimeStampedModel):
     title = models.CharField(max_length=1000, unique=True)
     description = models.TextField(blank=True, default='')
     reference = models.CharField(max_length=200, blank=True, null=True)
-    datetime = models.DateTimeField()
+    datetime = models.DateTimeField(db_index=True)
     kind = models.CharField(max_length=200, blank=True, default='')
     total_abstain = models.IntegerField()
     total_against = models.IntegerField()