[cmake][python] use `pip --upgrade` on install

Closes #81

See merge request !422

Allow to skip dune_python_package_install when pip is not found II

See merge request !399

[cmake][dune_add_test] Fix/dune add test cmake guard skip test

See merge request !409

This patch will always upgrade the Python package upon `make install`.

Previously, the Python package was only installed, if the package had not
been installed before. This violates the principle of least surprise as we
intuitively except `make install` to overwrite all files during the install
procedure.

move output operator to `Dune` namespace

See merge request !421

The function will usually be found via ADL.

If a complicated user defined command was specified, it didn't lead to the dummy
executable (that return 77) being run but the user defined command instead. This
patch makes sure that the correct command is executed which then marks the test
as skipped and not as failed. If a test is a parallel and tested with multiple
number of ranks all these test are shown as skipped.

run more tests in parallel

See merge request !411

Make CMake work with disabled version check.

See merge request !408

Do not assume that the complete message fits into tht buffer when sending in VariableSizeCommunicator

Closes #105

See merge request !416

If the buffer is small the we need to issue multiple sends and receive.
Unfortunately, the logic when sending was broken before this commit. It
simply always assumed that the buffer was larger than the complete message
to be send.

Feature/add cmake flags to dunecontrol

Closes #93

See merge request !378

It is now possible to pass -D...=... flags to CMake via configure-opts.
Bash- / Autotools-style variables like CC=.. or MPICC=.. are no longer
support in configure-opts.

Autotools are history, no need to check for libraries built by libtool.

[Doc] Reverse-engineer variablesizecommunicationtest

See merge request !415

Add editor hints to variablesizecommunitationtest.cc

See merge request !414

That test is a bit difficult to understand unless you know what it tries to
do, which is a problem if that is exactly what you're trying to figure out.
Here are my notes from trying that.

It seems to have magically escaped The Great Reindent, and of course uses
indent depth 4, not 2.

[dune_add_test] Do not check existance of EXPECT_COMPILE_FAIL targets.

Closes #100

See merge request !413

Fixes: #100.  See also: !404.

Those targets never exist -- instead, cmake is invoked during testing to
attempt to build them.

Before this commit setting DISABLE_CXX_VERSION_CHECK to true resulted
in the CMake error:

CMake Error at cmake/modules/CheckCXXFeatures.cmake:110 (if):
  if given arguments:

    "14" "GREATER"

  Unknown arguments specified
Call Stack (most recent call first):
  cmake/modules/CheckCXXFeatures.cmake:199 (dune_require_cxx_standard)
  cmake/modules/DuneMacros.cmake:690 (include)
  CMakeLists.txt:17 (dune_project)

Revert "Merge branch 'fix/dune-add-test-cmake-guard-skip-test' into 'master'"

See merge request !406

This reverts merge request !405

[cmake][dune_add_test] Set test property to depend on existence of target

Closes #100

See merge request !404

[cmake][dune_add_test] Fix cmake guard and skipping tests

See merge request core/dune-common!405

If a complicated user defined command was specified, it didn't lead to the dummy
executable (that return 77) being run but the user defined command instead. This
patch makes sure that the correct command is executed which then marks the test
as skipped and not as failed.

If the target was not found in the current state the test fails. With this
patch the ctest states "Not Run" and the name of the missing target.

fix disableCopyMove for empty arguments

See merge request !383

add fallback implementation of `is_invocable` and `is_invocable_r`

See merge request !393

Remove Pardiso from script am2cmake.py

See merge request !397