cell index was off by one.
Added use of apperance data.
Added code that makes sure that splats is at least the size of a voxel,
which should remove holes in the proxy-geometry where the geometry is
thin.
Changed from interval check to point-sampling along slice direction,
since splats now are guaranteed to be at least the size of a voxel.
Added proxy geometry group in render config, and added proxy resolution
value.
Added code that resizes renderlist grid.
Added check for source visibility when creating render lists.
Merge pull request #11 from sintefmath/renderlist_fixes

Renderlist fixes