Publish artifact to Sonatype OSS so it can be synced to Maven Central

This should resolve https://github.com/GabiAxel/spring-social-google/issues/5

Note there are further steps required here: https://docs.sonatype.org/display/Repository/Sonatype+OSS+Maven+Repository+Usage+Guide

Also, in compliance with Sonatype OSS practices I changed the groupId to com.gabiaxel.

I hope this is helpful in increasing the accessibility of this artifact as well as Spring Social!