new velocity boundary conditions for LBPU

the implementation is completely analogous to the CPU implementation
fixed the pressure tensor calculation for LB

and added a quite powerful testcase that
checks Couette and Poisseuille flow and
hydrostatic pressure in planar geometries
added pressure calculation for GPU
Merge branch 'lbgpu_development'
fixed pressure tensor for GPU LB and made testcase
Merge branch 'master' of https://github.com/kessel/espresso into kessel
Fixed requirements for new lb testcases.
Fixed auto-merge artefact.