radiationModels: Correct handling of ECont and make P1 and fvDOM consistent

Patch provided by Timo Niemi
Resolved bug-report http://www.openfoam.org/mantisbt/view.php?id=1636

This correction corresponds to option 3 of the options proposed by Timo:

Define both ECont and EDisp to be the total emission per surface area,
apply multiplication by 4 in cloudAbsorptionEmission model (the only
place that uses EDisp?). Do not multiply E in P1 at all, divide both
ECont and EDisp in fvDOM.