Allow comparative chart download

[TaiWilkin]

Overview

Updates the comparative chart download to correctly format the comparative "out of ten" chart titles.

Connects #118

Demo

Testing Instructions

• Select a combination of geographies for multiple years and geographies for one year, then select multiple years and a question of each type (stacked bar chart, grouped bar chart, and waffle / out-of-ten chart).
• Download the image for each chart.
• Download the CSV for each chart.
• Download the CSV for the full page.
• Repeat the above steps with only one year selected.
• The images and CSVs should download correctly and without errors.

[rajadain]

Taking a look now

[rajadain]

When generating a CSV for a stacked bar chart, the results have 2021 rows even though there are no values in the visual chart. Also, the numeric output is under Gender rather than Value:

[rajadain]

Actually, the above may be a problem in the configuration of some questions than a result of this PR. I see misquoted fields in the CSV here:

[TaiWilkin]

Thank you for reviewing! I have added a followup issue for the text issue here.