Updated shade mojo to use another artifactId

This pull request correspond to a mail i sent later on to maven-dev concerning one issue with maven-shade-plugin.
Although there is a `shadedArtifactId` field declared in ShadeMojo, it is absolutely unused.
I used that field to create a new project using that artifactId, instead of standard one.
I didn't wrote a test, as the current testing infrastructure seems strange to use. If a test is mandatory, I would gladly write one, provided someone mentors me on that subject.