add cloud messaging for android

[advans]

#22 add for android

[auser]

This looks AWESOME! I'll test it locally before I merge it, but it's looking great.

[auser]

@advans Are you interested in adding a demo usage of the Messaging API in the example app? https://github.com/fullstackio/FirestackApp

I can walk you through how it's created and how to extend it, if you're interested.

[Ehesp]

@advans Any idea how to handle notifications when the app isn't active (killed). It's logging the data, but doesn't do anything after that.

FSMessagingService: Message data payload: {body=Bar, title=Foo}