Android SDK

After some time I figured out how to implement the Android TestFlight SDK and this is the result.

I've never worked with TestFlight before, but I don't get steady entries at the TestFlight SDK debug console.
Sometimes the entries are extremely delayed, and sometimes they seem to never reach the TestFlight servers. ([Notice](http://help.testflightapp.com/customer/portal/articles/1279775-when-are-android-sdk-events-sent-))
So I'm not sure if the code or TestFlight is the problem. 

If someone could test this pull request first it would be great!