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
Also the whole point of this series of refactorings is to reduce duplication between plantain and pome to the minimum.