Consistent Versions for CodeGen

In the waLBerla CI a specific version of pystencils/lbmpy is set and tested. waLBerla should throw an error if it is used with an incompatible version of the codegen packages.

Furthermore, it might be better to define the codegen version somewhere globally. Doing so the CI could use this global defined version and an update of the codegen would result in only one change in the code furthermore, this could be used to throw the error.