[UIExplorer] Fix app icon so it actually shows up on the home screen

Summary:
Generated icons of the proper sizes so they show up on the home screen. It's not beautiful since the images have a transparent background but this also makes build warnings go away.

Closes https://github.com/facebook/react-native/pull/1267
Github Author: James Ide <ide@jameside.com>

Test Plan:  Run app, see icon on simulator home screen

Examples/UIExplorer/UIExplorer/Images.xcassets/AppIcon.appiconset/Contents.json

@@ -3,37 +3,37 @@
     {
       "size" : "29x29",
       "idiom" : "iphone",
-      "filename" : "uie_icon@2x.png",
+      "filename" : "Icon-Small@2x.png",
       "scale" : "2x"
     },
     {
       "size" : "29x29",
       "idiom" : "iphone",
-      "filename" : "uie_icon@2x-1.png",
+      "filename" : "Icon-Small@3x.png",
       "scale" : "3x"
     },
     {
       "size" : "40x40",
       "idiom" : "iphone",
-      "filename" : "uie_icon@2x-2.png",
+      "filename" : "Icon-40@2x.png",
       "scale" : "2x"
     },
     {
       "size" : "40x40",
       "idiom" : "iphone",
-      "filename" : "uie_icon@2x-3.png",
+      "filename" : "Icon-40@3x.png",
       "scale" : "3x"
     },
     {
       "size" : "60x60",
       "idiom" : "iphone",
-      "filename" : "uie_icon@2x-5.png",
+      "filename" : "Icon-60@2x.png",
       "scale" : "2x"
     },
     {
       "size" : "60x60",
       "idiom" : "iphone",
-      "filename" : "uie_icon@2x-4.png",
+      "filename" : "Icon-60@3x.png",
       "scale" : "3x"
     }
   ],