[Fix] PDF initialisation

PDFs can either be initialised in the pre- or post-collision state. Creating an LBM package always gave used the post-collision state by default. This imposes a problem especially when using mesh refinement, because the first step of the refinement is a streamCollide which requires a correct pre-collision state.

With this MR it is possible to choose the init state as input parameter and the pre-collision state is set as default.