Add missing docstrings

Add missing docstrings to modules, classes and functions. Refactor
existing docstrings that are not correctly formatted.

Issue: HIC-170
Change-Id: I766830259b897f8c2d931f3b53ce935e82b161fd
diff --git a/crashreport_stats/migrations/0002_version_and_versiondaily_with_defaults.py b/crashreport_stats/migrations/0002_version_and_versiondaily_with_defaults.py
index 29da259..aa14152 100644
--- a/crashreport_stats/migrations/0002_version_and_versiondaily_with_defaults.py
+++ b/crashreport_stats/migrations/0002_version_and_versiondaily_with_defaults.py
@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
-#
-# Set the default values for the Version and VersionDaily models.
+
+"""Migrations to set default values for the Version and VersionDaily models."""
+
 from __future__ import unicode_literals
 
 from django.db import migrations, models
@@ -8,6 +9,7 @@
 
 
 class Migration(migrations.Migration):
+    """Set the default values for the Version and VersionDaily models."""
 
     dependencies = [("crashreport_stats", "0001_initial")]