Add a single timeline to the project via the insert section list.
- Hook up delete functionality
- Add Timeline to the insert section list
- Disable Timeline in the insert section list if there is already one on the project
  - Add disable class on render
  - Listen for sections being added or removed and update the insert section list
- Add a helper to see if a project already contains at least one section of a particular type
- Make the project model and section collection accessible via the app