External feature pack for alternative Faces implementation integration

Replace the jsf/multi-installer functionality with a separate Galleon feature pack that users can use to provision a different JSF implementation. Something along the lines of https://github.com/wildfly-extras/wildfly-datasources-galleon-pack.

I think the target would be being able to install MyFaces. In the past jsf/multi-installer was also used to install alternative versions of Mojarra, but I don't know if that is still a meaningful use case.

A potential eventual home for this would be the wildfly-extras github organization. I don't have the impression this kind of thing has been used broadly enough to justify keeping it in the main WildFly repo.

I think a good approach to how to do it though would be to arrange the code so the pieces can be consumed by other feature packs than the one that's produced from the project. That is:

1) A maven module per jar archive produced.
2) One or more maven modules that produce a zip that contains other content that ends up being provisioned (module.xml files, Galleon related files).
3) A maven module for the feature pack itself, which is just a pom and a wildfly-feature-pack-build file.
4) A testsuite module that produces a artifact that can be consumed in other testsuites that want to test the functionality from 1) and 2) when integrated into their own installations (a la MicroProfile TCKs.)