Simplified the app

/cc @ciaranarcher @scott2211 

I've made a number of changes which simplifies the application and solves the issues with naming and the back button.

We now have the following controllers:

`Movies.ListsController` - this represents a list of lists at `http://localhost:8000/#/lists`
`Movies.ListController` - this represents a single list - `http://localhost:8000/#/lists/pk94l`
`Movies.MovieController` - this represents a single movie in a list and manages editing the movie and setting its `watched` state.

The routes are no longer nested, we should only nest routes when we have a master-detail UI:

```javascript
this.resource('lists');
this.resource('list', { path: '/lists/:list_id' })
```

I haven't touched the tests, they will have to be updated. Let me know if you've any questions.