fix add_dumux_test for use with Dune 2.6

See merge request !659

add_dumux_test forwards to dune_add_test. Since Dune 2.6, this takes
only the "real" command behind COMMAND, the arguments to that command
have to follow behind CMD_ARGS.

[2padaptive] Fix pressure reconstruction for 2p adaptionhelper

See merge request !657

For some grids, e.g. UGGrid, the father element
is identical to the son element.
It is therefore not a good idea to use the
adaptedValue containers for the father and
for the son element since they might be also identical.
This has been changes such that the adaptedValues
are no longer modified in the reconstruction routine.

[headercheck] add missing includes

See merge request !655

Do nothing and give warning if scotch wasn't found

See merge request !651

[CHANGELOG] add link to multidomain README

See merge request !649

(cherry picked from commit f9cc226c)

update CHANGELOG.md, bump handbook version

See merge request !648

[headercheck] add missing includes

See merge request !647

[multidomaingrid] include <numeric> before multidomaingrid.hh

See merge request !646

Otherwise, std::partial_sum is not found for newer STL versions.
In principle, this should be fixed upstream...

update list of copyright holders

See merge request !645

[2pnc] remove unused variable

See merge request !644

[sequential] remove unused variables from MPFA-L velocity models

See merge request !643

[doc] update the parameter list

See merge request !642

[2p][adaptive] use right privars for vol vars update

See merge request !635

For cell-centered scheme, the primary variables in the reconstruction
were not divided by the number of children that composed the primary
variables in a father element. This does not have an effect here as the
helper class and the tests only consider incompressible fluids. Furthermore,
the problem would only appears if in one refinement some elements get refined more
than one level. However, for the sake of readability it should be correct here.

[cpgrid] fix grid creator, cleanup fvelementgeometry

See merge request !624

The static Opm::Deck variable was handled incorrectly in the
grid creator. Fix the behavior by initializing the variable
directly.

Also perform a cleanup of the FVElementGeometry by removing the
lines associated with local coordinates and removing an unused
local variable.

[CHANGELOG.md] Update

See merge request !622

[doxygen][sequential] cleanup and make more consistent with actual implementation and implicit doxygen

[moduleutil] Print and throw error if something went wrong while checking the module version

See merge request !613

Fix/include heat capacity in enthalpy for other gases

See merge request !608

Fix/include heat capacity in enthalpy for air

See merge request !611

Nitrogen already had a heat capacity function, however, it was calculated differently for the other gases.

Part II: reference solutions