Add a cumulative chart

Checked on Watsi's transparency docs tonight, noticed they have a chart
of cumulative volume:

https://docs.google.com/spreadsheet/pub?key=0Ah3wJ9CRQzyHdDZSaEF1X1JsRm1yZ251d0RQZ0VmRGc&gid=12

Adding the same to our charts page.
Bump version to 7.2.23
Bump version to 7.2.23-dev