[Example App] implement more complex layout for grid view

### Some ideas:

- [x] Orthogonal sections (Horizontally scrolling sections)
- [ ] Groups
- [ ] Search/Filter (add a search bar and filter results, see _Implementing Modern Collection Views_ below)

#### Maybe? Eventually?
- Collapsing headers (see #33)
- Layout changes? (see #92)

> ⚠️ **No need to do this all at once.** Small PRs with one new feature are best. 😊

### Examples and Sample code:

- [Implementing Modern Collection Views](https://developer.apple.com/documentation/uikit/views_and_controls/collection_views/implementing_modern_collection_views)
- [Updating Collection Views Using Diffable Data Sources](https://developer.apple.com/documentation/uikit/views_and_controls/collection_views/updating_collection_views_using_diffable_data_sources)
- [Getting Started with UI​Collection​View​Compositional​Layout](https://lickability.com/blog/getting-started-with-uicollectionviewcompositionallayout/)