Put a visualization of Tor Browser downloads and updates on the Metrics website

We have the following items on the metrics team roadmap:

• 2017-01: Add a visualization of Tor Browser downloads to Metrics. (Sponsor X 6.3. Metrics, part 1)
• 2017-01: Finalize visualizations of Tor Browser downloads on Metrics based on user feedback. (Sponsor X 6.3. Metrics, part 2)

We can re-use existing work from #20008 (moved) here where we defined a database schema and wrote an importer.

And we already have two prototypes (1 and 2) which are based on RStudio's Shiny, which we can't use here, but which we can use for inspiration. To be clear, what we do here will be less shiny, because we're stuck with our not-very-interactive graphing engine. But we cannot solve that now.

I'll attach early results in a second.