Add custom collection view layout example project

examples/CustomCollectionView/Sample/Images.xcassets/LaunchImage.launchimage/Contents.json

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+{
+  "images" : [
+    {
+      "orientation" : "portrait",
+      "idiom" : "iphone",
+      "filename" : "Default-568h@2x.png",
+      "minimum-system-version" : "7.0",
+      "subtype" : "retina4",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "iphone",
+      "scale" : "1x",
+      "orientation" : "portrait"
+    },
+    {
+      "idiom" : "iphone",
+      "scale" : "2x",
+      "orientation" : "portrait"
+    },
+    {
+      "orientation" : "portrait",
+      "idiom" : "iphone",
+      "filename" : "Default-568h@2x.png",
+      "subtype" : "retina4",
+      "scale" : "2x"
+    },
+    {
+      "orientation" : "portrait",
+      "idiom" : "iphone",
+      "minimum-system-version" : "7.0",
+      "scale" : "2x"
+    }
+  ],
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  }
+}