adding solvent to BlackOilFluidState

[GitPaean]

The main motivation is to support other development which requires that we can create FluidState for the wellbore.

Under certain circumstances, there might be only be Solvent in side the wellbore. With the master branch, solvent saturation is stored in blackoilsolventmodules.hh .

With the new design, some implementation might be able to be done in different ways, but this PR is mostly moving things around.

[GitPaean]

jenkins build this opm-simulators=6939 failure_report please

[GitPaean]

The only failure is https://ci.opm-project.org/job/opm-common-PR-builder/9571/testReport/junit/(root)/default/compareECLFiles_flow_SPE5CASE1/

Comparing SEQNUM ...  done.
Comparing INTEHEAD ...  done.
Comparing LOGIHEAD ...  done.
Comparing DOUBHEAD ...  done.
Comparing IGRP ...  done.
Comparing SGRP ...  done.
Comparing XGRP ...  done.
Comparing ZGRP ...  done.
Comparing IWEL ... 

Keyword: IWEL, origin Restart, sequence 43

Value index                 = 318
(first value, second value) = (-1, 3)

Program threw an exception: [/build/test_util/EclRegressionTest.cpp:183] Non floating point values not identical 
Comparing '/build/deps/opm-tests/spe5/opm-simulation-reference/flow/SPE5CASE1' to '/build/default/build-opm-simulators/tests/results/flow+spe5/SPE5CASE1'.

Loading EGrid /build/deps/opm-tests/spe5/opm-simulation-reference/flow/SPE5CASE1.EGRID  ....  done.
Loading EGrid /build/default/build-opm-simulators/tests/results/flow+spe5/SPE5CASE1.EGRID  ....  done.
comparing grids 

Comparing egrid files 

Dimensions              ...  done.
Active cells            ...  done.
X, Y and Z coordinates  ...  done.
NNC indices             ...  done.

Loading INIT file /build/deps/opm-tests/spe5/opm-simulation-reference/flow/SPE5CASE1.INIT  .... done
Loading INIT file /build/default/build-opm-simulators/tests/results/flow+spe5/SPE5CASE1.INIT  .... done

not totally sure what it is about. Maybe @bska can give some suggestions. Thanks.