Build: create a consumer (flatten) pom and remove all build specific items

[brenuart]

The project should ideally publish a consumer pom free of all build specific items. This can be accomplished by the flatten-maven-plugin and choosing the ossrh flatten style.

There is one issue tho: the flatten pom should be post processed by the shade plugin to remove the shaded dependencies. However, it happens that the shade plugin builds its dependency-reduced pom from the in-memory model and is therefore no aware of the flattening already performed by the flatten plugin. An alternate strategy is to:

• use XLST to remove shaded dependencies from the flatten pom
• tell the shade plugin to not build a dependency reduced pom and not touch the pom file already included in the jar when shading it