Aggregate coverage reports for entire project

What about setting cobertura to aggregate for the entire build? This way instead of generating one report for each module we get the overall report in one place (src/parent/target/site/cobertura/).

Individual reports are still available by specifying a single project in the build command.

    $ mvn cobertura:cobertura -f src/parent/pom.xml -pl :geogit-core