Resolve "JSON output for timing"

Closes #65

See merge request walberla/walberla!127

Enable raytracing of ConvexPolygon pe body

See merge request walberla/walberla!131

Fix pe::findContainingProcess for bodies within -1*epsilon of a block edge

See merge request walberla/walberla!128

pe_coupling geometry: squirmers are spheres too

See merge request walberla/walberla!129

The necessary to_json(...) function are used. One can create a json
object by e.g. "nlohmann::json ttjson = nlohmann::json(tt)" with tt
being a timing tree

Fixed force scaling in first time step of some test cases

See merge request walberla/walberla!126

Add reader for raw files

See merge request walberla/walberla!125

Fix in SCIterator

See merge request walberla/walberla!123

- generalized PdfFieldPackInfo to be used with a stencil template
  argument instead of a LatticeModel
- PdfPackInfo now available from Python

Add image generation using a raytracer

See merge request walberla/walberla!89

Pe-Coupling Classes Splits

See merge request walberla/walberla!120

Utilities and Extensions to the geometry functionality

See merge request walberla/walberla!117