Fix VP sensor DE -> PV association

The sensor DetElement was being associated with the wrong PlacedVolume. It was associated with the placement of lvDet within lvSensor, while it should be associated with the placement of lvSensor in lvLadder. This is fixed here.

In addition, there is a fix to the number of the ladder DetElement's.

And also some improvements to the naming of various PlacedVolume's - this is partly to ease the comparison of the DD4hep and DetDesc geometries.

The checksums are updated accordingly.