[Examples] CustomCollectionView in Swift3 (#2591)

* new Swift example

* removed asyncDataSource and asyncDelegate. Also using collectionNode methods instead of collectionView

* Fixing the folder structure

* Updated with @george-gw feedback. Thanks George.

examples/CustomCollectionView-Swift/Sample/Assets.xcassets/image_8.imageset/Contents.json

@@ -0,0 +1,21 @@
+{
+  "images" : [
+    {
+      "idiom" : "universal",
+      "filename" : "image_8.jpg",
+      "scale" : "1x"
+    },
+    {
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  }
+}