graphing DPKG source v3 adoption

Given that now we can upload DPKG source v3 packages to the archive, prodded by Lucas and Martin, I've added yet another page to my Debian graph/stats collection: namely stats about DPKG source v3 usage in the archive.

This time, I've done even less work than the other pages: Lucas was already providing the actual data via a UDD CGI. So thank him, I'm basically just aggregating/mirroring the graphs for bandwidth reasons.

Of course, I've also added the new page to the stats index on wiki.d.o.