this is necessary because tables now must be queried using
EclipseState instead of directly. This implies that EclipseState can
be instantiated in the first place...
TODO (?): allow EclipseState instatiation for decks without a grid.
The pvt interface is extended to handle wet-gas systems:
1. rvSat is added as a function in the PVT interface
2. SinglePvtLiveGas computes the pvt values and its derivatives
3. The old rbub variable is changed to rsSat for clearity
4. The new interface is tested in test_blackoilfluid with data from
liveoil.DATA and wetgas.DATA
