Added toaster plugin for Android

I have added a plugin to show messages using the native Android toaster.

I have tested it on Android 4.0.4 and 2.1-update1.

Here's a screenshot of it working on 4.0.4:

![Android-Toaster-Plugin-Screenshot](https://f.cloud.github.com/assets/152131/15542/f48a70f0-4785-11e2-8818-18d957d1201a.png)