Feature Idea: Download CSV #9

[ch-sander]

Maybe allow to download a CSV (in addition to PNG #9, or just the JSON generated to not reparse to CSV if awkward). Why?

1. There might be preset data users want to download (i.e. data they have not uploaded)
2. The selection of items could filter the CSV rows (Feature Idea: Improve Selection #13)
3. additional columns generated (Feature Idea: Numerical Aggregation and clustering #6) are added at runtime and don't feature in the source data