Handle Percentage Charts

[TaiWilkin]

Overview

More clearly expresses the data in percentage charts by setting their limit to 100, and formatting ticks and tooltips as percentages.

Adds locale formatting to non-percentage grouped bar charts.

Also switches the format of keys for charts to prevent duplicate key warnings.

Connects #56

Demo

Notes

We chose to leave the current types as-is, even though hours and null type charts are handled identically at the moment, in order to allow for differentiation in the future if desired.

Testing Instructions

• In the deploy preview, select several percentage-type questions, hours-type questions, and null-type questions.
• Confirm that the percentage charts show percentages in the axis and the tooltip, and that they are set to limits of 0%-100%.
• Confirm that the hours- and null-type questions are working as before with auto-calculated limits, and that the numbers are formatted reasonably.

[TaiWilkin]

Rebased to manage merge conflicts.

[TaiWilkin]

Thank you for the review!