Integrate Cobertura to coveralls.io

Related:
* http://www.petrikainulainen.net/programming/maven/creating-code-coverage-reports-for-unit-and-integration-tests-with-the-jacoco-maven-plugin/
* http://blog.eluder.org/2013/06/code-coverage-for-github-hosted-java-projects-with-coveralls/
* http://avandeursen.com/2012/12/21/line-coverage-lessons-from-junit/ => good notes about the ~5% of code that is never reached (e.g. private constructors, case default, exception catch, ...)
* http://www.coding-stories.com/blog/2012/01/23/couverture-des-tests-dintegration-avec-jacoco-maven-et-sonar/
* http://linsolas.free.fr/wordpress/index.php/2011/07/calculer-sa-couverture-de-code-par-les-tests-dintegration/
* store in a dedicated sonarqube instance: https://gist.github.com/Wulfspider/11309089