[WIP] Created a quiz service for loading the topics/quizzes hierarchy, and implemented the most important pieces of the topics sidebar (using the abn-tree directive)

Still lots to do:

- Selecting a topic doesn't actually do anything yet (doesn't update the main content area)
- Can't add or delete topics yet (or reorder)
- Dumping debug info on the page
- Needs a lot of code cleanup
- e2e tests broken