Faults

This PR will introduce the transmissibility effects of MULTFLT and FAULTS in the TransMult container:

1. Added classes FaultFace, Fault and FaultCollection
2. Added internal GridProperty<double> fields for all of face directions in TransMult container. This is implemented with a 'instantiate on demand' semantics - a bit uncertain about that?
3. Added the fault functionality to EclipseState.