Fix fluctuating LB with zero centered pdf storage

See merge request !186

Fix Musker's law

See merge request !185

Fix GPU copy kernels in periodicity handling

Closes #45

See merge request !182

Added a copy kernel, which can be used to transfer data from a source field to a destination field.

See merge request !181

[FIX] PSM generation

See merge request !180

Implements a getter function for the strain rate tensor

See merge request !179

Integrate force calculation in wall boundaries

See merge request !177