Make all graph data available as CSV

Right now, we provide links to CSV files that graphs are based on. But in some cases it requires non-trivial data wrangling skills to obtain the data in the graph, which is less usable than it could be.

What we could do instead is generate CSV files based on the graph and selected parameters. This will enable users to quickly obtain the data in a graph and further process it using tools of their choice.

I already wrote this code and deployed it but did not merge it yet. I'm going to post a branch in a minute. My plan is to merge later today. Rushing this a bit, because it's something that should still go into the February report.