Allow Question Category Select-All/None

Overview

Allows users to select/deselect all questions in a category by toggling the category checkbox.

Connects #60

Checks

In the deploy preview, select a region or country and continue to questions.
Open a category and select a question. The category should move to an indeterminate checkbox.
Select the category checkbox. All questions in the category should be selected.
Deselect one question in the category. The category should move to an indeterminate state.
Reselect the question and the checkbox should move to a selected state.
Deselect the checkbox. All questions in the category should be deselected.
Manually select all questions in the category. The category should be marked selected.
Manually deselect all questions in the category. The category should be marked unselected.
Select/deselect various combinations of categories and questions across categories; the selection should behave as expected across categories.