Resolve "Replace deprecated CUDA APIs"

Closes #71

See merge request walberla/walberla!157

- information from CMake to codegen: double/float, OpenMP, ...

- More flexibility for the user to implement custom checkpointing

MPICH2 apparently expects a non-const pointer for blocklenghts whereas
other MPIs expect const pointer -> removed const to work with all

- intel 19 internal bug when using auto, and implicit capture in lambdas

- LB on GPU, Uniform Grid Benchmark app
- helper class to schedule tasks to multiple CUDA streams

- comparison to old CPU transfer communication included

- CUDA compiler has problems to compile external json library
- timing pool is included by BlockForest, and previously timing pool
  included JSON library

previously the ghost layer was aligned

Features:
   - uses generated pack infos for packing & unpacking directly on GPU
   - can directly send GPU buffers if cuda-enabled MPI is available,
     otherwise the packed buffers are transfered to CPU first
   - communication hiding with cuda streams: communication can be run
     asynchronously - especially useful when compute kernel is also
     split up into inner and outer part

- added RAII classes for CUDA streams and events
- equivalence test that checks if generated CPU and GPU (overlapped)
  versions are computing same result as normal waLBerla LBM kernel

- templated buffer classes allow the buffer systems to work with custom
  buffers, e.g. buffers of GPU memory

Fix for numerical issue in EPA

See merge request walberla/walberla!154

Add waLBerla-conforming .editorconfig

See merge request walberla/walberla!156

Change stringstream name in macros to hopefully avoid name clashes

See merge request walberla/walberla!155

Resolve "add sent and received bytes to BufferSystem"

Closes #75

See merge request walberla/walberla!153

integrated g++8

See merge request walberla/walberla!150

extended OpenMPWrapper with runtime functions

See merge request walberla/walberla!149