Make Data page dynamic

The Data page in the Metrics Portal (http://metrics.torproject.org/data.html) lists all metrics data that we have. This page is a static HTML page that is updated whenever we have new data. This means we need to update it at least once a month to list the new monthly descriptor tarballs. Once we switched the Metrics Portal to JSP/Servlets, this page should be generated dynamically with whatever data is available.