Merge pull request 'Fix cuda::pow() bugfix, while passing doubles explicitly.'...

Merge pull request 'Fix cuda::pow() bugfix, while passing doubles explicitly.' (#67) from peters/VirtualFluids_dev:bugfix/cuda_pow into develop

Reviewed-on: https://git.irmb.bau.tu-bs.de/VirtualFluids/VirtualFluids_dev/pulls/67

This pow-solution is not optimal but will work hopefully. The kernel performance will probably be decreased, because "double" calculations are 3-5 times slower compared to floating point operations.