Redesign Scoring Rubric

This MR significantly changes the markup, CSS, and JS of the Scoring Rubric, adding:

• Improved design
• Formal extensibility pattern using CSS variables
• Additional “active” styling to range markers
• Ability to click on range markers to jump the range to that one
• Use BEM class names for constructing the rubric

Note: The current value marker was removed from the default design, but if we want it back, we can enable this rule (e.g., .scoringrubric .rubric__current-value-wrapper--visible).

Before	After