Fix unintialized warning in Config.h when compiling with undef. sanitizer

Closes #39

See merge request walberla/walberla!170

Fix error when writing fluid field VTK output with OpenMPI version > 2.x.x

See merge request walberla/walberla!173

Added module description for pecoupling

See merge request walberla/walberla!172

- proper escaping of braces when passing JSON to python
- pass information if walberla was built with CUDA to pystencils
  to support apps that use GPU optionally

- allows for nested execution flow (i.e. solver loop inside time loop)
- timing tree integration
- parallel CUDA stream support

- WALBERLA_BUILD_WITH_OPENMP was never defined

Add forgotten incrementor in iterator macro

See merge request walberla/walberla!171

Fix typo in iterator macros

See merge request walberla/walberla!169

when compiling with undefined behaviour sanitizer and gcc 8.2
a -Werror=maybe-uninitialized warning appears when using the const refs
the std::move variant does not have this problem

Use for loops instead of while loops in iterator macros

See merge request walberla/walberla!168

- for example conda ships this old MPI version

Su Viscoelasticity

See merge request walberla/walberla!146

Fix VTK output for bodies with infinite mass

See merge request walberla/walberla!167

Only call MPI_Finalize if we actually called MPI_Init

See merge request walberla/walberla!166

Call target_link_libraries with PUBLIC keyword if necessary

See merge request walberla/walberla!164

CMake: Make doc target and additional CXX warning flags switchable

See merge request walberla/walberla!165

Remove boost::bind from tutorial

See merge request walberla/walberla!161

remove mscv 2015 from ci and use cuda 9.0 in ubuntu 16.04

Closes #79

See merge request walberla/walberla!162

remove clang 3 and intel 2016

Closes #79

See merge request walberla/walberla!160