adapt construction of to EclipseWriter

i.e., don't pass around the UnstructuredGrid object directly, but use
the "generic" interface which is also used in the case Dune::CpGrid.
Update phase condition vector from primary variables.

This is necessary as an interim measure, since the phase condition vectors are
still used in property calculations.
pass the EclipseState and the PhaseUsage objects to EclipseWriter
Merge pull request #167 from andlaus/do_not_pass_shared_ptr_to_EclipseWriter

pass a reference to the UnstructuredGrid to EclipseWriter instead of a shared_ptr
Added test to ensure active gas phase.
Merge pull request #169 from atgeirr/update-condition

Update phase condition vector from primary variables.

This resolves #168.
pass the DerivedGeology to the simulators

this was decided to be a good idea by [at]bska. (If I interpreted him
correctly, obviously.)
DerivedGeology: pass the EclipseState object to its constructor

this is required to implement pore volume and permeability multipliers
as discussed with [at]bska and [at]joakim-hove.

Note that this implies that the DerivedGeology class can't be
instantiated anymore if there is no EclipseState object. Thus all code
paths and tests that don't load a deck are removed by this patch. If
this is undesireable, there are two options: First, don't require
EclipseState for DerivedGeology which would imply to make the about 10
required multiplier functions part of the
BlackoilPropertiesAdInterface, or second, one can copy-and-paste the
DerivedGeology class as it was before this patch, derive from a newly
introduced DerivedGeologyInterface and pass DerivedGeologyInterface
objects to the simulator. IMHO, the second solution would be a bit
better but it would involve substantial overhead to implement and to
maintain it.

Anyway, in the mean time simulators cannot be instantiated without
decks.
implement pore volume and permeability multipliers

this means that the NTG, MULTPV and MULT[XYZ]-? keywords are now
supported.

Actually FAULTS and MULTFAULT are supported too, but that's abstracted
away by opm-parser's TransMult class. (Kudos to [at]joakim-hove for
implementing this.)
add a unit test for the implementation of transmissibilty multipliers in DerivedGeology

for the legacy C-style grid the unit test is more or less complete (it
does not test FAULTMULT and NNC, etc, but these could be added with
sufficient determination), for Dune::CpGrid it currently does not
really check anything because I have not found a good way for CpGrid
to produce the "global" intersection index of an intersection...