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/admin.py b/crashreport_stats/admin.py
index db5b576..a5a720e 100644
--- a/crashreport_stats/admin.py
+++ b/crashreport_stats/admin.py
@@ -1,4 +1,4 @@
-"""Register models for admin site"""
+"""Register models for admin site."""
 from django.contrib import admin
 from crashreport_stats.models import (
     Version,