Corrected stress correction and a different way to implement the force externally from the kernel. Initial conditions for jet.

adds wrapper for gpu WIP

Now MultiphasePressureFilterLBMKernel pressure update is also corrected (wrong fiel in previous commit).

corrects pressure update in MultiphaseTwoPhaseFieldsPressureFilterLBMKernel, MultiphasePressureFilterCompressibleAirLBMKernel and MultiphasePressureFilterCompressibleAirLBMKernel. MultiphasePressureFilterCompressibleAirLBMKernel is not yet different from MultiphasePressureFilterCompressibleAirLBMKernel and hence not yet compressible.