Create a Maven specific abstraction for Artifact use within Maven

There's no point in just flipping all references from Maven Artifact to Mercury without protecting ourselves from this sort of thing in the future. This will also allow us to remove the few straggling bits in Mercury that are Maven specific like scopes and classifiers.

Once this is created then we can seriously consider plugging in Mercury behind it. We have a complete and total clusterfuck as it stands as the components for artifact manipulation and the use of Artifact are just used scatter shot through out the whole codebase. A direct transition to Mercury would make for a goat fuck we can avoid.