* clean up

* do some clean-up as well

Feature/test angeli

See merge request !653

* Adapt fluidsystem
* make some variables const

Cleanup/remove default components prop

See merge request !658

Improve properties

See merge request !630

* do not inherit from ModelProperties
* use CMAKE_GUARD to skip test if alugrid not found

* add new test, only checking a simple scvf
* improve free-flow specific test

* use CellCenterPrimaryVariables instead of PrimaryVariables

* minimal scvf implementation, contains dofIndex() and localFaceIndex()

* set type in FreeFlow properties
* clean-up header
* return const ref instead of copies

* use correct includes and inheritance

* include dumux/common/properties.hh
  instead of dumux/common/basicproperties.hh
* do not inherit from LinearSolverTypeTag and
  NumericModel anymore because those type tags don't exist anymore

* header does not exist anymore