Added object to single section selection delegate callback

Summary:
- Updated selectionDelegate to pass through the model object
- Changelog entry under 3.0.0 as is breaking change

Try saying single section selection 10 times quick
Dabbing my left toe into some ObjC, so apologies if I violate years of rules

- [ ] Update documentation internally

Closes #396

- [x] All tests pass. Demo project builds and runs.
- [x] I added tests, an experiment, or detailed why my change isn't tested.
- [x] I added an entry to the `CHANGELOG.md` for any breaking changes, enhancements, or bug fixes.
- [x] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/master/.github/CONTRIBUTING.md)
Closes https://github.com/Instagram/IGListKit/pull/397

Differential Revision: D4406213

Pulled By: rnystrom

fbshipit-source-id: ba468fa49e75823796a47da6ed7f0e8957db3d75

Examples/Examples-iOS/IGListKitExamples/ViewControllers/SingleSectionViewController.swift

@@ -69,9 +69,11 @@ final class SingleSectionViewController: UIViewController, IGListAdapterDataSour
     
     // MARK: - IGListSingleSectionControllerDelegate
     
-    func didSelect(_ sectionController: IGListSingleSectionController) {
+    func didSelect(_ sectionController: IGListSingleSectionController, with object: Any) {
         let section = adapter.section(for: sectionController) + 1
-        let alert = UIAlertController(title: "Section \(section) was selected \u{1F389}", message: nil, preferredStyle: .alert)
+        let alert = UIAlertController(title: "Section \(section) was selected \u{1F389}",
+                                      message: "Cell Object: " + String(describing: object),
+                                      preferredStyle: .alert)
         alert.addAction(UIAlertAction(title: "Dismiss", style: .default, handler: nil))
         present(alert, animated: true, completion: nil)
     }