Prevent a traceback when Nagios is not configured

Out of the box you get a traceback on the home page without this change.
This should make local development easier
Fix default graphite URL
Add Y-axis labels to all existing graphs

Some of these are 'unknown' until I figure out what they are
Add payments data

This is just a rough start, we can expand later
Merge pull request #12 from kumar303/webpay

Add payments stats