kw VAPPARS etc

- Note that the EQUIL-based initialization depends on PR opm-core#607 for proper initialization of surface volumes.
- Re-introducing the old singular matrix fix seems to mitigate some problems concerning infinite residuals.  (Indicates that PR opm-autodiff#144 did not completely solve the singular matrix problem?)
- VAPPARS: Inclusion of sat_oil derivatives in jacobians currently disabled as it is not observed have any noticeable effect on the convergence behavior.  This may change during further testing, or if other, more dominating problems concerning the convergence behavior are removed.