Move emulation model definition out of POM

[kennedy-mindermann]

Right now the emulation model definition exists in both POM and IOM. Move it out of POM.

[acostarelli]

In progress in #160 . It's unclear to me if we want this for Sienna 1.0 @luke-kiernan @jd-lara ? (And same for #152 )

[luke-kiernan]

It's not core functionality, but imo it's central enough to the UI that it's worth doing. Conceptually, model definitions belong better in IOM. There's nothing power systems specific about them. Moving them breaks reverse-compatibility, so needs to happen in a major release