Update .gitignore to support Android Studio project

Signed-off-by: Ricardo Leitão <rleitao@lqd.io>
Change project structure to Android Studio

Signed-off-by: Ricardo Leitão <rleitao@lqd.io>
Update Readme with gradle / maven setup

Signed-off-by: Ricardo Leitão <rleitao@lqd.io>