WIP: Refactor contributor graph

What does this MR do?

Heavily refactors the contributor stat graph.

This is actually more than a refactor, it changes some logic.

It uses ES6 classes instead of JS's poor substitution for OO. It uses lambdas instead of the function(_this){ function... }(scope) pattern.

More info coming later.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?