Improve number formatting on platform-admin page

Minor changes to the number formatting for the `/platform-admin` page to
- Show the complaint percentage to 2 decimal places. (The number of
complaints is often below 0.0% so 1 decimal place isn't useful)
- Format the numbers in the status boxes to use a comma as a thousands
separator.

app/statistics_utils.py

@@ -52,6 +52,13 @@ def get_formatted_percentage(x, tot):
     return "{0:.1f}".format((float(x) / tot * 100)) if tot else '0'
 
 
+def get_formatted_percentage_two_dp(x, tot):
+    """
+    Return a percentage to two decimal places
+    """
+    return "{0:.2f}".format((float(x) / tot * 100)) if tot else '0'
+
+
 def statistics_by_state(statistics):
     return {
         'sms': {