Pome JS tests now part of build

Moved rdf/src to rdf/rdf_common_jvm/src so that IDE's work nicer. Otherwise, I have just got pome compiling OK and the tests pass.

I have also used my plugin https://github.com/InTheNow/sbt-scalajs that allows scalajs to test and compile as per a scala project - i,e

sbt test
I have the feeling we are not talking about the same thing. I refer explicitly to what was done in https://github.com/w3c/banana-rdf/commit/b8f4c076f52547af0627234e70b97f55454f6639 .

This PR is reverting that. **I do not want to revert that**. Changing what gets aggregated in `root` does not help splitting the modules, nor it helps reducing the redundancies between them. Or I'll admit I don't understand the reasonning.