Added total-downloads.py example

It's just a simple example of chart to present total number of downloads: installers or packages.

Before launching this script there is a necessity to clone appropriate source of data (this could be available only for internal developers of Continuum Analytics).
> Seems like the issue is a missing header in `pkgs/2014-05-01.pkgs.internalpanel.data.gz`.

Yes, You have to pull latest data from the repository. There is a commit which corrects this situation.