Use visualization name for CSV export filename

[oweizman]

Currently all tables that are downloaded are named table.csv, both when downloading the raw and the formatted form. It would be useful to have the the csv named after the visualization name and contain other useful meta-data.

[rashidkpc]

This probably isn't too hard. What should we do in the case that the visualization is not named? I guess we can just fall back to "table"

[oweizman]

Maybe fall back to something like Viz of index_name, still more informative than just table.