Add maven-integration

Then simply run `maven clean package` to generate the apk.

Need extra dependency to artifact android.support:compatibility-v4:11 because
of usage of SparseArrayCompat (official com.google.android:support-v4:11 is
not available in the central naven repository). To get this dependency, use
the github project maven-android-sdk-deployer
(https://github.com/mosabua/maven-android-sdk-deployer).