Support tintColor and thumbTintColor for Switch on Android

Summary:
**Motivation**

`Switch` on Android doesn't allow changing the colors unlike iOS. Changing the colors is desirable in a lot of cases to match the brand colors.

The PR adds support for the `tintColor`, `onTintColor` and `thumbTintColor` props on Android, which more or less behave the same as iOS. The only difference is `tintColor` styles the border color on iOS, whereas it styles the background color on Android.

**Test plan (required)**

Run UIExplorer with the changes, and ensure that the switch example works properly. Here are screenshots from iOS and Android to compare.

![image](https://cloud.githubusercontent.com/assets/1174278/22018002/b05d6482-dcd2-11e6-9c00-f55a71d6ce29.png)

![image](https://cloud.githubusercontent.com/assets/1174278/22018012/b923e974-dcd2-11e6-8d4e-86994f5a66e6.png)

cc brentvatne
Closes facebook/react-native#11940

Differential Revision: D4427491

fbshipit-source-id: 16c569d2e2261daaea93fffa83198f8f6b59a6c8

UIExplorer/js/SwitchExample.js

@@ -147,15 +147,12 @@ var examples = [
   {
     title: 'Switches are controlled components',
     render(): React.Element<any> { return <Switch />; }
-  }
-];
-
-if (Platform.OS === 'ios') {
-  examples.push({
+  },
+  {
     title: 'Custom colors can be provided',
     render(): React.Element<any> { return <ColorSwitchExample />; }
-  });
-}
+  }
+];
 
 exports.title = '<Switch>';
 exports.displayName = 'SwitchExample';