[ReactNative] Export EdgeInsetsPropType and PointPropType

Summary:
Added some more exports to React that are either necessary or often useful for component authors.

Closes facebook#262
Github Author: James Ide <ide@jameside.com>

Test Plan: Imported from GitHub, without a `Test Plan:` line.

Libraries/react-native/react-native.js

@@ -65,6 +65,10 @@ var ReactNative = Object.assign(Object.create(require('React')), {
   Platform: require('Platform'),
   requireNativeComponent: require('requireNativeComponent'),
 
+  // Prop Types
+  EdgeInsetsPropType: require('EdgeInsetsPropType'),
+  PointPropType: require('PointPropType'),
+
   addons: {
     LinkedStateMixin: require('LinkedStateMixin'),
     Perf: undefined,