Fixed a bug with top grid kernel normalization, this reduces errors a bit.
A non-cubic grid is now extended to a cubic grid in the density calculation. This should reduce artefacts due to TF truncation.
Added a new (undocumented and internal) parameter that forces grid centering on the specified refinement region also in unigrid mode. This should in the future also obey that the shift comes in multiples of the top grid cells (which are however unknown).
Fixed a bug in the generic output plugin that caused non-cubic grids to be cut to cubic grids.
