analytics: Separate private messages from group private messages.

This makes it possible for our graphs to show the group private
message counts as separate from 1:1 private messages.

Fixes #4102.

analytics/migrations/0010_clear_messages_sent_values.py

@@ -0,0 +1,27 @@
+# -*- coding: utf-8 -*-
+from django.db.backends.postgresql_psycopg2.schema import DatabaseSchemaEditor
+from django.db.migrations.state import StateApps
+from django.db import migrations
+
+def clear_message_sent_by_message_type_values(apps, schema_editor):
+    # type: (StateApps, DatabaseSchemaEditor) -> None
+    UserCount = apps.get_model('analytics', 'UserCount')
+    StreamCount = apps.get_model('analytics', 'StreamCount')
+    RealmCount = apps.get_model('analytics', 'RealmCount')
+    InstallationCount = apps.get_model('analytics', 'InstallationCount')
+    FillState = apps.get_model('analytics', 'FillState')
+
+    property = 'messages_sent:message_type:day'
+    UserCount.objects.filter(property=property).delete()
+    StreamCount.objects.filter(property=property).delete()
+    RealmCount.objects.filter(property=property).delete()
+    InstallationCount.objects.filter(property=property).delete()
+    FillState.objects.filter(property=property).delete()
+
+class Migration(migrations.Migration):
+
+    dependencies = [('analytics', '0009_remove_messages_to_stream_stat')]
+
+    operations = [
+        migrations.RunPython(clear_message_sent_by_message_type_values),
+    ]