Create a grid layout for IGList

Summary:
Rebase from #140:

Create a flow layout for IGList that does not newline sections. Closes #3

- [x] Minimum inter-item spacing
- [x] Minimum line spacing
- [x] Constant item size with constant layout time
- [x] Update layout on insert/delete/move
- [x] Unit Test
Closes https://github.com/Instagram/IGListKit/pull/225

Differential Revision: D4211469

Pulled By: rnystrom

fbshipit-source-id: f4710dbf195701098ac50f94b6b2aa8c801b2a83

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

@@ -15,15 +15,48 @@
 import UIKit
 import IGListKit
 
-final class StoryboardViewController: UIViewController, IGListAdapterDataSource {
-
+final class StoryboardViewController: UIViewController, IGListAdapterDataSource, StoryboardLabelSectionControllerDelegate {
+    
     @IBOutlet weak var collectionView: IGListCollectionView!
     
     lazy var adapter: IGListAdapter = {
         return IGListAdapter(updater: IGListAdapterUpdater(), viewController: self, workingRangeSize: 0)
     }()
     
-    lazy var words = "Maecenas faucibus mollis interdum Praesent commodo cursus magna, vel scelerisque nisl consectetur et".components(separatedBy: " ")
+    lazy var people = [
+        Person(pk: 1, name: "Littlefinger"),
+        Person(pk: 2, name: "Tommen Baratheon"),
+        Person(pk: 3, name: "Roose Bolton"),
+        Person(pk: 4, name: "Brienne of Tarth"),
+        Person(pk: 5, name: "Bronn"),
+        Person(pk: 6, name: "Gilly"),
+        Person(pk: 7, name: "Theon Greyjoy"),
+        Person(pk: 8, name: "Jaqen H'ghar"),
+        Person(pk: 9, name: "Cersei Lannister"),
+        Person(pk: 10, name: "Jaime Lannister"),
+        Person(pk: 11, name: "Tyrion Lannister"),
+        Person(pk: 12, name: "Melisandre"),
+        Person(pk: 13, name: "Missandei"),
+        Person(pk: 14, name: "Jorah Mormont"),
+        Person(pk: 15, name: "Khal Moro"),
+        Person(pk: 16, name: "Daario Naharis"),
+        Person(pk: 17, name: "Jon Snow"),
+        Person(pk: 18, name: "Arya Stark"),
+        Person(pk: 19, name: "Bran Stark"),
+        Person(pk: 20, name: "Sansa Stark"),
+        Person(pk: 21, name: "Daenerys Targaryen"),
+        Person(pk: 22, name: "Samwell Tarly"),
+        Person(pk: 23, name: "Tormund"),
+        Person(pk: 24, name: "Margaery Tyrell"),
+        Person(pk: 25, name: "Varys"),
+        Person(pk: 26, name: "Renly Baratheon"),
+        Person(pk: 27, name: "Joffrey Baratheon"),
+        Person(pk: 28, name: "Stannis Baratheon"),
+        Person(pk: 29, name: "Hodor"),
+        Person(pk: 30, name: "Tywin Lannister"),
+        Person(pk: 31, name: "The Hound"),
+        Person(pk: 32, name: "Ramsay Bolton")
+    ]
     
     override func viewDidLoad() {
         super.viewDidLoad()
@@ -34,13 +67,20 @@ final class StoryboardViewController: UIViewController, IGListAdapterDataSource
     //MARK: IGListAdapterDataSource
     
     func objects(for listAdapter: IGListAdapter) -> [IGListDiffable] {
-        let items: [IGListDiffable] = words as [IGListDiffable]
-        return items
+        return people
     }
     
     func listAdapter(_ listAdapter: IGListAdapter, sectionControllerFor object: Any) -> IGListSectionController {
-        return StoryboardLabelSectionController()
+        let sectionController = StoryboardLabelSectionController()
+        sectionController.delegate = self
+        return sectionController
     }
     
     func emptyView(for listAdapter: IGListAdapter) -> UIView? { return nil }
+    
+    func removeSectionControllerWantsRemoved(_ sectionController: StoryboardLabelSectionController) {
+        let section = adapter.section(for: sectionController)
+        people.remove(at: Int(section))
+        adapter.performUpdates(animated: true)
+    }
 }