Attach the build POM and simplify the build/consumer implementation

The build/consumer implementation was initially written in SAX, later rewritten using Xpp3, then Stax, but this implementation is quite complex with a big drawback in that it affects multiple places in the code where the models are loaded.

Rewriting the transformation on top of the object model remove those problems, at the cost of loosing the comments in the consumer POM.  The build POM is thus attached with the original unmodified POM, with build classifier to differentiate.