- recent GCC version produce error when "-isystem /usr/include" is added
  to command line. Error is: '#include_next <math.h>' not found
- the removed "hack" added the cuda include dir with "-isystem" to
  the CUDA compiler arguments to prevent warnings from boost header
  -> currently there seem to be no warnings generated from boost headers
     so "hack" is removed

Add Intel 2019 compiler to CI

See merge request !138

Add Intel Compiler 2018 to CI

See merge request walberla/walberla!133

Resolve "DEM benchmarking tool"

Closes #51

See merge request walberla/walberla!84

Clang tidy performance checks

See merge request walberla/walberla!137

Clang7

See merge request walberla/walberla!136

Additional get() and operator() for GhostLayerFieldAdaptor

See merge request walberla/walberla!135

Interpolator fix

See merge request walberla/walberla!134