Unfortunately the CMake logic for quad math detection was overwriting the Quadmath
package from Dune and had to be removed. This removes all quadmath code from
Dumux and uses the quadmath implementation of Dune instead (Dune::Float128)
which is based on the same library.

Due to !1905

Timo Koch authored 4 years ago and Ned Coltman committed 4 years ago

FluidSystem::getMainComponent returns the main componet index of the phase.
This doesn't actually make sense for the tracer models which why this commit also
* removes getMainComponent for tracer fluid systems (Changelog amended)
* guards all occurences of getMainComponent in code that works for tracer too
with constexpr if

* With this patch you only include what you need
* The header gridmanager.hh includes all specializations
  as convenience. This makes this patch also fully backwards-compatible