Also added computeStaticData() helper called by both constructors.
It is still possible to use the other constructor for an incompressible case,
by passing a null pointer for the rock_comp argument.
Most significant changes:
- Single solve() call used for all cases (with or without gravity,
with or without rock compressibility). This is intentionally
similar to CompressibleTpfa::solve().
- Constructor take a property object and computation of necessary total
mobilities etc. moved inside class.
- Optional constructor args for rock compressibility, gravity, wells,
boundary conditions (null pointer accepted) and source terms (empty
vector accepted).
- Nonlinear iterations for the compressible rock case now handled inside
IncompTpfa. This part intentionally made similar to CompressibleTpfa.
