Fix bugs in saturation initialisation and helpers.
Add another test deck for initialisation.

This deck includes capillary functions.
Add test case for capillary inversion.
Add saturation computation to and rename computer class.

Opm::equil::DeckDependent::PhasePressureComputer ->
Opm::equil::DeckDependent::PhasePressureSaturationComputer
Add test case with capillary transition region.