Improve model hook of project/tasks/index

# Problem

The current `model` hook does a lot of `async`, `await`, and `RSVP.all` weirdness. We should either:

- just query for and assign the project as the model, then have the task lists and the project users be a computed on the controller. ~2-4 hours, depending on tests, etc
- get the project using `modelFor`, then have the model hook explicitly make two queries, one for all members of that project, the other for all task lists of that project. our API would need to support those filters on those respective endpoints. ~~4-6 hours