Gradle-i-fy the library

Add's the gradle build framework to allow for much easier integration into new android projects.
Also allows this sample to be used with Android Studio in a more fluent way.

*I realise this probably won't get merged in as it moves every single file, but it highlights how easy it is to move to gradle. Just look at the diff for the two build.gradle files at the top of the 'files changed'.*