[DO NOT MERGE YET] XD-783b: Alternate MR layout

Inspired by https://github.com/spring-projects/spring-xd/pull/414, but using the same approach as our current ResourceMR.

Allows us to leverage boot tooling (maven/gradle plugin)

Named "2" for now, until we transition our modules to this layout (using a DelegatingMR).

Things to consider:
* Should we fail/warn when multiple candidates for type+name are found?
* The root of each archive itself should be considered a classpath root too (similar to what is done in https://github.com/spring-projects/spring-xd/pull/414) but work on ModuleOptions will bring more light on this